World War I (abbreviated WWI or WW1; also known as the First World War, the Great War, and the War to End All Wars) was a fought chiefly in from 1914 to 1918. 
The scale and intensity of the conflict were unprecedented, with more men fighting and more casualties in action than any prior human conflict. About 70 million took part in the fighting,  including 60 million Europeans.   New technologies - , better , advanced , , and - increased the scale of the carnage. The war claimed over 40 million , including approximately 20 million and military .  Many of the events attendant upon the war - , , and - increased the misery.
The war had for politics and diplomacy in the rest of the 20th century. The war resulted in the collapse and fragmentation of the Empire, the , and the . The was overthrown, and Germany lost territory. As a consequence, the maps of Europe and the Middle East were re-drawn; ancient were replaced by or . For the first time, an international body, the , was created to prevent war ever occurring again. The , and the instability of new nations, were important leading towards twenty years later.
The causes of the war can be traced to the in 1871,  and the uneasy balance of power among the European in the opening years of the 20th century. Additional spurs to conflict included continuing over the in the 19th century; growing economic, military and colonial competition between Britain and Germany; and the continuing instability of Austro-Hungarian rule in the .
The proximate trigger for the war was the 28 June 1914 , heir to the throne, by a . Austria-Hungary's demands for revenge against the led to the activation of a series of alliances which within weeks saw most European powers at war. Because of the global empires of many European nations, the war soon spread worldwide.
The war was fought between two major alliances. The initially consisted of , the , , and their associated empires and dependencies. Numerous other states joined these allies, most notably in August 1914, in April 1915, and the in April 1917. The , so named because of their central location on the European continent, initially consisted of and and their associated empires. The joined the Central Powers in October 1914, followed a year later by . By the conclusion of the war, only The , , , the , and remained officially neutral among the European countries, though several may have provided financial and material support to one side or the other.
The fighting of the war mostly took place along several fronts that broadly encircled the European continent. The was marked by a system of trenches, breastworks, and fortifications separated by an area known as .  These fortifications stretched 475 miles (more than 600 kilometres)  and precipitated a style of fighting known as . On the , the vastness of the eastern plains and the limited railroad network prevented the stalemate of the Western Front, though the scale of the conflict was just as large. There was heavy fighting on the , the and the ; there were also hostilities at sea and in the air.
- Main article: Origins of World War I
On 28 June 1914, , a student, shot and killed , heir to the in . Princip was a member of , a group whose aims included the unification of the and independence from Austria-Hungary. The set into motion a series of that eventually escalated into full-scale war.  Austria-Hungary demanded action by to punish those responsible and, when Austria-Hungary deemed Serbia had not complied, declared war. Major European powers were at war within weeks because of overlapping agreements for and the complex nature of international alliances.
The German industrial base had, by 1914, overtaken that of Britain, though Germany did not have the commercial advantages of a large empire. In the years running up to the war a race to possess the strongest navy arose between Britain and Germany, each country building large numbers of dreadnoughts. The naval race between Britain and Germany was intensified by the 1906 launch of , a revolutionary craft whose size and power rendered previous battleships obsolete. Britain also maintained a large naval lead in other areas particularly over Germany and Italy.
described the arms race as "a self-reinforcing cycle of heightened military preparedness."  David Herrmann viewed the shipbuilding rivalry as part of a general movement in the direction of war.  The revisionist , however, argued Britain's ability to maintain an overall lead signified this was not a factor in the oncoming conflict. 
The cost of the arms race was felt in both Britain and Germany. The total arms spending by the six Great Powers (Britain, Germany, France, Russia, Austria-Hungary and Italy) increased by 50% between 1908 and 1913. 
Plans, distrust, and mobilization
Closely related is the thesis adopted by many that the mobilization plans of Germany, France and Russia automatically escalated the conflict. Due to the complicated logistics required to activate, move, and supply millions of troops, each nation's mobilization plans were worked out well in advance, creating a situation where mobilization almost required the country to immediately go on the attack. In particular, historian emphasized the inherently aggressive nature of the , which outlined a two-front strategy. Fighting on two fronts meant Germany had to eliminate one opponent quickly before taking on the other. It called for a strong right , to seize Belgium and cripple the by pre-empting its mobilization. After the attack, the would rush east by railroad and quickly destroy the slowly mobilizing Russian forces. 
France's Plan XVII envisioned a quick thrust into the , Germany’s industrial heartland, which would in theory cripple Germany's ability to wage a modern war.
Russia's Plan 19 foresaw a concurrent mobilization of its armies against Austria-Hungary, Germany, and the Ottomans, while Plan 19 Revised saw Austria-Hungary as the main target, reducing the initial commitment of troops against East Prussia.  
All three plans created an atmosphere in which speed was thought to be one of the determining factors for victory. Elaborate timetables were prepared; once mobilization had begun, there was little possibility of turning back. Diplomatic delays and poor communications exacerbated the problems.
Also, the plans of France, Germany and Russia were all biased toward the offensive, in clear conflict with the improvements of defensive firepower and entrenchment.
Militarism and autocracy
and others blamed the war on .  Some argued that and military élites had too much power in countries such as Germany, Russia, and Austria-Hungary.  War was thus a consequence of their desire for and disdain for . This theme figured prominently in propaganda.   When the German effort was failing in 1918, calls grew for the abdication of rulers such as  , as well as an end to aristocracy and militarism in general. This platform provided some justification for the American entry into the war when the Russian Empire surrendered in 1917.
The Allies consisted of Great Britain and France, both democracies, fighting the Central Powers, which included Germany, Austro-Hungary, and the Ottoman Empire. Russia, one of the Allied Powers, was an empire until 1917, but it was opposed to the subjugation of by Austro-Hungary. Against this backdrop, the view of the war as one of democracy versus dictatorship initially had some validity, but lost credibility as the conflict continued.
Wilson hoped the and would secure a lasting peace. Borrowing a thesis from , he described the war as a "war to end all war". He was willing to side with France and the Britain to this end, despite their own militarism.
famously  put most of the blame on Germany's aristocratic leaders. He argued that the German leaders thought they were losing power and time was running out. The German social democratic party had won several elections, increasing their voting share and had by 1912 become the most represented party in Germany. While the elected institutions had little power compared with the Kaiser it was feared that some form of political revolution was imminent. Russia was in midst of a large scale military build-up and reform which was to be completed in 1916-17. A war would unite Germany and defeat Russia before this. In his later works Fischer went further and argued  that Germany had planned the war in 1912.
Historian Samuel R. Williamson has emphasized the role of Austria-Hungary. Convinced that Serbian nationalism and Russian Balkan ambitions were disintegrating a monarchy comprising eleven different nationalities, Austria-Hungary hoped for a limited war against Serbia and that the strong German support would force Russia to keep out of the war and weaken its Balkan prestige. 
Balance of power
One of the goals of the foreign policies of the Great Powers in the pre-war years was to maintain the 'Balance of Power' in Europe. This evolved into an elaborate network of secret and public alliances and agreements. For example, after the (1870–71), Britain seemed to favour a strong Germany, as it helped to balance its traditional enemy, France. After Germany began its naval construction plans to rival that of Britain, this stance shifted. France, looking for an ally to balance the threat created by Germany, found it in Russia. Austria-Hungary, facing a threat from Russia, sought support from Germany.
When World War I broke out, these treaties only partially determined who entered the war on which side. Britain had treaties with France or Russia, entering the war on their side. Italy had a treaty with both Austria-Hungary and Germany, yet did not enter the war with them; Italy later sided with the Allies. Perhaps the most significant treaty of all was the initially defensive pact between Germany and Austria-Hungary, which Germany in 1909 extended by declaring that Germany was bound to stand with Austria-Hungary even if it had started the war. 
asserted that was responsible for the war. He drew upon the of and English economist , who predicted that unlimited competition for expanding markets would lead to a global conflict.  Lenin and others pointed out that the dominant economic position of Great Britain was threatened by the rapid rise of German industry; However, Germany did not have the commercial advantages of a major empire, and was therefore inevitably going to fight Britain for more economic space for German capital. This argument was popular in the wake of the war and assisted in the rise of . Lenin argued that the banking interests of various capitalist-imperialist powers orchestrated the war. 
, American Secretary of State under , believed that were the root cause of both World War I and World War II. In 1944, he helped design the to reduce trade barriers and eliminate what he saw as the cause of the conflicts.  
Ethnic and political rivalries
A war between Austria-Hungary and Serbia was considered inevitable, as Austria-Hungary’s influence waned and the movement grew. The rise of ethnic nationalism coincided with the growth of Serbia, where anti-Austrian sentiment was perhaps most fervent. Austria-Hungary had occupied the former Ottoman province of , which had a large Serb population, in 1878. It was by Austria-Hungary in 1908. Increasing nationalist sentiment also coincided with the decline of the . Russia supported the Pan-Slavic movement, motivated by ethnic and religious loyalties and a rivalry with Austria dating back to the . Recent events such as the and a century-old dream of a also motivated St. Petersburg. 
Myriad other geopolitical motivations existed elsewhere as well, for example France's loss of and in the helped create a sentiment of irredentist revanchism in that country. France eventually allied itself with Russia, creating the likelihood of a for Germany.
- See also:
July crisis and declarations of war
- Main article: July Ultimatum
The Austro-Hungarian government used the assassination of as a pretext to deal with the Serbian question, supported by Germany. On 23 July 1914, an was sent to Serbia with ten demands, some so extreme that the Serbian reply included reservations and rejected the sixth demand. The Serbians, relying on support from Russia, removed acceptance of the sixth key demand (the draft reply had accepted it), and also ordered mobilization. In response, Austria-Hungary issued a declaration of war on 28 July. Initially, Russia ordered partial mobilization, directed at the Austrian frontier. On 31 July, after the Russian General Staff informed the Czar that partial mobilization was logistically impossible, a full mobilization was ordered. The , which relied on a quick strike against France, could not afford to allow the Russians to mobilize without launching an attack. Thus, the Germans declared war against Russia on 1 August and on France two days later. Germany then violated the neutrality of by advancing through it on the way to Paris. This brought the British Empire into the war, as Britain had guaranteed Belgium's neutrality in treaties arising from the of 1830. With this, five of the six European powers were now involved in the largest continental European conflict since the . 
Confusion among the Central Powers
The strategy of the Central Powers suffered from miscommunication. Germany had promised to support Austria-Hungary’s invasion of Serbia, but interpretations of what this meant differed. Austro-Hungarian leaders believed Germany would cover its northern flank against Russia. Germany, however, envisioned Austria-Hungary directing the majority of its troops against Russia, while Germany dealt with France. This confusion forced the to divide its forces between the Russian and Serbian fronts.
- Main article: African theatre of World War I
Some of the first clashes of the war involved British, French and German colonial forces in Africa. On 7 August, French and British troops invaded the German protectorate of . On 10 August German forces in attacked ; sporadic and fierce fighting continued for the remainder of the war.
- Main article: Serbian Campaign (World War I)
The Serbian army fought the against the invading Austrians, beginning on 12 August, occupying defensive positions on the south side of the and rivers. Over the next two weeks Austrian attacks were thrown back with heavy losses, which marked the first major Allied victory of the war and dashed Austrian hopes of a swift victory. As a result, Austria had to keep sizable forces on the Serbian front, weakening its efforts against Russia.
German forces in Belgium and France
- Main article: Western Front (World War I)
Initially, the Germans had great success in the (14 August–24 August). Russia, however, attacked in and diverted German forces intended for the . Germany defeated Russia in a series of battles collectively known as the First (17 August – 2 September), but this diversion exacerbated problems of insufficient speed of advance from rail-heads not foreseen by the German . Originally, the Schlieffen Plan called for the right flank of the German advance to pass to the west of Paris. However, the capacity and low speed of horse-drawn transport hampered the German supply train, allowing French and to finally halt the German advance east of Paris at the (5 September–12 September). The Central Powers were thereby denied a quick victory and forced to fight a war on two fronts. The German army had fought its way into a good defensive position inside France and had permanently incapacitated 230,000 more French and British troops than it had lost itself. Despite this, communications problems and questionable command decisions cost Germany the chance of obtaining an early victory.
Asia and the Pacific
- Main article: Asian and Pacific theatre of World War I
occupied (later ) on 30 August. On 11 September the landed on the island of (later New Britain), which formed part of . seized Germany's colonies and after the , the German coaling port of , in the Chinese peninsula. Within a few months, the Allied forces had seized all the German territories in the Pacific.
Trench warfare begins
|This section is missing or needs .|
Using helps guard against copyright violations and factual inaccuracies. (February 2008)
- Main article: Western Front (World War I)
Military tactics before World War I had failed to keep pace with advances in technology. These changes resulted in the building of impressive defence systems, which out-of-date tactics could not break through for most of the war. was a significant hindrance to massed infantry advances. , vastly more lethal than in the 1870s, coupled with , made crossing open ground very difficult. The Germans introduced ; it soon became used by both sides, though it never proved decisive in winning a battle. Its effects were brutal, causing slow and painful death, and poison gas became one of the most-feared and best-remembered horrors of the war. Commanders on both sides failed to develop tactics for breaching entrenched positions without heavy casualties. In time, however, technology began to produce new offensive weapons, such as the . Britain and France were its primary users; the Germans employed captured Allied tanks and small numbers of their own design.
After the , both and German forces began a series of outflanking maneuvers, in the so-called . Britain and France soon found themselves facing entrenched German forces from to Belgium's coast. Britain and France sought to take the offensive, while Germany defended the occupied territories; consequently, German trenches were generally much better constructed than those of their enemy. Anglo-French trenches were only intended to be 'temporary' before their forces broke through German defenses. Both sides attempted to break the stalemate using scientific and technological advances. In April 1915 the Germans used for the first time (in violation of the ), opening a six kilometre (four mile) hole in the Allied lines when British and French colonial troops retreated. closed the breach at the . At the , Canadian and troops took the village of .
The endured the bloodiest day in its history, suffering 57,470 casualties and 19,240 dead on 1 July 1916, the of the . Most of the casualties occurred in the first hour of the attack. The entire Somme offensive cost the British Army almost half a million men.  Neither side proved able to deliver a decisive blow for the next two years, though protracted German action at throughout 1916, combined with the Entente's failure at the ,  brought the exhausted French army to the brink of collapse. Futile attempts at frontal assault, a rigid adherence to an ineffectual method,  came at a high price for both the British and the French poilu (infantry) and led to , especially during the . Throughout 1915–17, the British Empire and France suffered more casualties than Germany, due both to the strategic and tactical stances chosen by the sides. At the strategic level, while the Germans only mounted a single main offensive at , the Allies made several attempts to break through German lines. At the tactical level, the German defensive doctrine was well suited for trench warfare, with a relatively lightly defended "sacrificial" forward position,  and a more powerful main position from which an immediate and powerful counter-offensive could be launched. This combination usually was effective in pushing out attackers at a relatively low cost to the Germans.  In absolute terms, of course, the cost in lives of men for both attack and defense was astounding.
Ludendorff wrote on the fighting in 1917, "The 25th of August concluded the second phase of the Flanders battle. It had cost us heavily…. The costly August battles in Flanders and at Verdun imposed a heavy strain on the Western troops. In spite of all the concrete protection they seemed more or less powerless under the enormous weight of the enemy’s artillery. At some points they no longer displayed the firmness which I, in common with the local commanders, had hoped for. The enemy managed to adapt himself to our method of employing counter attacks… I myself was being put to a terrible strain. The state of affairs in the West appeared to prevent the execution of our plans elsewhere. Our wastage had been so high as to cause grave misgivings, and had exceeded all expectation."
On the battle of the Menin Road Ridge Ludendorff wrote: "Another terrific assault was made on our lines on the 20 September…. The enemy’s onslaught on the 20th was successful, which proved the superiority of the attack over the defence. Its strength did not consist in the tanks; we found them inconvenient, but put them out of action all the same. The power of the attack lay in the artillery, and in the fact that ours did not do enough damage to the hostile infantry as they were assembling, and above all, at the actual time of the assault."  Around 800,000 soldiers from the British Empire were on the Western Front at any one time.  1,000 battalions, occupying sectors of the line from the to the , operated on a month-long four-stage rotation system, unless an offensive was underway. The front contained over 9,600 kilometres (5,965 mi) of trenches. Each battalion held its sector for about a week before moving back to support lines and then further back to the reserve lines before a week out-of-line, often in the or areas.
In the 1917 the only significant British military success was the capture of by the under and . The assaulting troops were able for the first time to overrun, rapidly reinforce and hold the ridge defending the coal-rich plain. 
- Main article: Naval Warfare of World War I
At the start of the war, the German Empire had scattered across the globe, some of which were subsequently used to attack Allied merchant shipping. The British systematically hunted them down, though not without some embarrassment from its inability to protect Allied shipping. For example, the German detached light cruiser Emden, part of the East-Asia squadron stationed at Tsingtao, seized or destroyed 15 merchantmen, as well as sinking a Russian cruiser and a French destroyer. However, the bulk of the —consisting of the armoured cruisers and , light cruisers and and two transport ships—did not have orders to raid shipping and was instead underway to Germany when it encountered elements of the British fleet. The German flotilla, along with , sank two armoured cruisers at the , but was almost completely destroyed at the in December 1914, with only Dresden escaping. 
Soon after the outbreak of hostilities, Britain initiated a naval of Germany. The strategy proved effective, cutting off vital military and civilian supplies, although this blockade violated generally accepted international law codified by several international agreements of the past two centuries.  Britain mined international waters to prevent any ships from entering entire sections of ocean, causing danger to even neutral ships.  Since there was limited response to this tactic, Germany expected a similar response to its unrestricted submarine warfare.  The 1916 (German: Skagerrakschlacht, or "Battle of the Skagerrak") developed into the largest naval battle of the war, the only full-scale clash of battleships during the war. It took place on 31 May–1 June 1916, in the off . The Kaiserliche Marine's High Seas Fleet, commanded by Vice Admiral , squared off against the Royal Navy's Grand Fleet, led by Admiral Sir . The engagement was a standoff, as the Germans, outmaneuvered by the larger British fleet, managed to escape and inflicted more damage to the British fleet than they received. Strategically, however, the British asserted their control of the sea, and the bulk of the German surface fleet remained confined to port for the duration of the war.
German attempted to cut the supply lines between North America and Britain.  The nature of submarine warfare meant that attacks often came without warning, giving the crews of the merchant ships little hope of survival.  The United States launched a protest, and Germany modified its rules of engagement. After the notorious sinking of the passenger ship in 1915, Germany promised not to target passenger liners, while Britain armed its merchant ships, placing them beyond the protection of the "cruiser rules" which demanded warning and placing crews in "a place of safety" (a standard which lifeboats did not meet).  Finally, in early 1917 Germany adopted a policy of , realizing the Americans would eventually enter the war.  Germany sought to strangle Allied sea lanes before the U.S. could transport a large army overseas.
The U-boat threat lessened in 1917, when merchant ships entered escorted by destroyers. This tactic made it difficult for U-boats to find targets, which significantly lessened losses; after the introduction of and , accompanying destroyers might actually attack a submerged submarine with some hope of success. The convoy system slowed the flow of supplies, since ships had to wait as convoys were assembled. The solution to the delays was a massive program to build new freighters. Troop ships were too fast for the submarines and did not travel the North Atlantic in convoys.  
World War I also saw the first use of in combat, with launching in a successful raid against the hangars at in July 1918, as well as for antisubmarine patrol. 
War in the Balkans
- Main articles: Balkans Campaign (World War I), Serbian Campaign (World War I), and Macedonian front (World War I)
Faced with Russia, Austria-Hungary could spare only one third of its army to attack Serbia. After suffering heavy losses, the Austrians briefly occupied the Serbian capital, . A Serbian counterattack in the , however, succeeded in driving them from the country by the end of 1914. For the first ten months of 1915, Austria-Hungary used most of its military reserves to fight Italy. German and Austro-Hungarian diplomats, however, scored a coup by convincing to join in attacking Serbia. The Austro-Hungarian provinces of , and provided troops for Austria-Hungary, invading Serbia as well as fighting Russia and Italy. allied itself with Serbia.
Serbia was conquered in a little more than a month. The attack began in October, when the Central Powers launched an offensive from the north; four days later the Bulgarians joined the attack from the east. The Serbian army, fighting on two fronts and facing certain defeat, retreated into , halting only once in order to make a stand against the Bulgarians. The Serbs suffered defeat near modern day in the  . Montenegro covered the Serbian retreat toward the Adriatic coast in the in 6-7 January 1916, but ultimately the Austrians conquered Montenegro, too. Serbian forces were evacuated by ship to .
In late 1915 a Franco-British force landed at in Greece, to offer assistance and to pressure the government to declare war against the Central Powers. Unfortunately for the Allies, the pro-German dismissed the pro-Allied government of , before the Allied expeditionary force could arrive.
After conquest, Serbia was divided between Austro-Hungary and Bulgaria. Bulgarians commenced bulgarization of the Serbian population in their occupation zone, banishing and the . After forced conscription of the Serbian population into the Bulgarian army in 1917, the Uprising began. Serbian rebels liberated for a short time the area between the mountains and the river. The uprising was crushed by joint efforts of Bulgarian and Austrian forces at the end of March 1917.
The Macedonian Front proved static for the most part. Serbian forces retook part of Macedonia by recapturing on 19 November 1916. Only at the end of the conflict were the Entente powers able to break through, after most of the German and Austro-Hungarian troops had withdrawn. The suffered their only defeat of the war at the but days later, they decisively defeated British and forces at the , avoiding occupation. Bulgaria signed an on 29 September 1918.
- Main article: Middle Eastern theatre of World War I
The joined the Central Powers in the war, the secret having been signed in August 1914. It threatened Russia's territories and Britain's communications with via the . The British and French opened overseas fronts with the (1915) and campaigns. In Gallipoli, the successfully repelled the British, French and (ANZACs). In , by contrast, after the disastrous (1915–16), British Imperial forces reorganised and captured in March 1917. Further to the west, in the , initial British setbacks were overcome when was captured in December 1917. The , under Field Marshal , broke the Ottoman forces at the in September 1918.
Russian armies generally had the best of it in the . , supreme commander of the Turkish armed forces, was ambitious and dreamed of conquering . He was, however, a poor commander.  He launched an offensive against the Russians in the Caucasus in December 1914 with 100,000 troops; insisting on a frontal attack against mountainous Russian positions in winter, he lost 86% of his force at the . 
The Russian commander from 1915 to 1916, General , drove the Turks out of most of the southern Caucasus with a string of victories.  In 1917, Russian assumed command of the Caucasus front. Nicholas planned a railway from to the conquered territories, so that fresh supplies could be brought up for a new offensive in 1917. However, in March 1917, (February in the pre-revolutionary Russian calendar), the Czar was overthrown in the and the began to fall apart. In this situation, the army corps of realigned themselves under the command of General , with as a civilian commissioner of the . The front line had three main divisions: , , and . Another regular unit was under Colonel Korganian. There were Armenian (more than 40,000  ) accompanying these main units.
The (described in Lawrence of Arabia) was a major cause of the 's defeat. The revolts started with the by Sherif Hussain of with the help of Britain in June 1916, and ended with the Ottoman surrender of Damascus. the Ottoman commander of showed stubborn resistance for over two and half years during the .
Along the border of Italian Libya and British Egypt, the tribe, incited and armed by the Turks, waged a small-scale guerrilla war against Allied troops. According to Martin Gilbert's The First World War, the British were forced to dispatch 12,000 troops to deal with the Senussi. Their rebellion was finally crushed in mid-1916.
- Main article: Italian Campaign (World War I)
Italy had been allied with the German and Austro-Hungarian Empires since 1882 as part of the . However, the nation had its own designs on Austrian territory in , and . had a secret 1902 pact with France, effectively nullifying its alliance.  At the start of hostilities, Italy refused to commit troops, arguing that the was defensive in nature, and that Austria-Hungary was an aggressor. The Austro-Hungarian government began negotiations to secure Italian neutrality, offering the French colony of in return. The Allies made a counter-offer in which Italy would receive the Alpine province of and territory on the coast after the defeat of Austria-Hungary. This was fomalised by the . Further encouraged by the Allied invasion of Turkey in April 1915, Italy joined the and declared war on Austria-Hungary in May. Fifteen months later Italy declared war on Germany.
Militarily, the Italians had numerical superiority. This advantage, however, was lost, not only because of the difficult terrain in which fighting took place, but also because of the strategies and tactics employed. , a staunch proponent of the frontal assault, had dreams of breaking into the Slovenian plateau, taking and threatening . It was a plan, which had no realistic chance of success in an age of barbed wire, machine guns, and indirect artillery fire, combined with hilly and mountainous terrain.
On the Trentino front, the Austro-Hungarians took advantage of the terrain, which favoured the defender. After an initial strategic retreat, the front remained largely unchanged, while Austrian and (German wikipedia) engaged Italian in bitter hand-to-hand combat throughout the summer. The Austro-Hungarians counter-attacked in the , towards Verona and Padua, in the spring of 1916 (Strafexpedition), but made little progress.
Beginning in 1915, the Italians under Cadorna mounted eleven offensives on the along the , north-east of . All eleven offensives were repelled by the Austro-Hungarians, who held the higher ground. In the summer of 1916, the Italians captured the town of . After this minor victory, the front remained static for over a year, despite several Italian offensives. In the autumn of 1917, thanks to the improving situation on the Eastern front, the Austrians received large numbers of reinforcements, including German and the elite . The Central Powers launched a crushing offensive on 26 October 1917, spearheaded by the Germans. They achieved a victory at . The Italian army was routed and retreated more than 100 km (60 miles) to reorganise, stabilizing the front at the . Since in the Battle of Caporetto Italian Army had heavy losses, the Italian Government called to arms the so called '99 Boys (Ragazzi del '99), that is, all males who were 18 years old. In 1918, the Austro-Hungarians failed to break through, in a series of battles on the , finally being decisively defeated in the in October of that year. Austria-Hungary surrendered in early November 1918.   
- Further information:
Fighting in India
The war began with an unprecedented outpouring of loyalty and goodwill towards the United Kingdom from within the mainstream political leadership, contrary to initial British fears of an Indian revolt. India under British rule contributed massively to the British war effort by providing men and resources. This was done by the Indian Congress in hope of achieving self-government as India was very much under the control of the British. The United Kingdom disappointed the Indians by not providing self-governance, leading to the Era in Indian history. About 1.3 million Indian soldiers and labourers served in , , and the , while both the Indian government and the princes sent large supplies of food, money, and ammunition. In all 140,000 men served on the Western Front and nearly 700,000 in the Middle East. 47,746 Indian soldiers were killed and 65,126 wounded during World War I. 
Indian independence movement
and remained hotbeds of . Terrorism in Bengal, increasingly closely linked with the unrests in Punjab, was significant enough to nearly paralyse the regional administration. Also from the beginning of the war, expatriate Indian population, notably in , and , headed by the and the respectively, attempted to trigger insurrections in India on the lines of the with , German and Turkish help in a massive conspiracy that has since come to be called the . The conspiracy attempts to rally the Amir of Afghanistan against British India, starting a political process in that country that culminated three years later in the assassination of Amir Habibullah and precipitation of the . A number of failed attempts at mutiny were made in India, of which the and the remain most notable. This movement was suppressed by means of a massive international counter-intelligence operation and draconian political acts (including the ) that lasted nearly ten years.   
The Ghadarites also attempted to organise incursions from the western border of India, recruiting Indian prisoners of war from , , . Ghadarite rebels, led by Amba Prasad, fought along with Turkish forces in and in . Plans were made in to organise a campaign from Persia, through , to Punjab. These forces were involved skirmishes that captured the frontier city of Karman, taking into custody the British consul. 's campaign in Persia was directed mostly against these composite forces. It was at this time that the and his brother were recruited into the British War effort. However, the Aga Khan's brother was captured and shot dead by the rebels, who also successfully harassed British Forces in in Afghanistan, confining British forces to in Baluchistan, later moving towards . They were able to take control of the coastal towns of Gawador and Dawar. The Baluchi chief of Bampur, having declared his independence from the British rule, also joined the Ghadarite forces. It was not before the war in Europe turned for the worse for Turkey and was captured by the British forces that the Ghadarite forces, their supply lines starved, were finally dislodged. They retreated to regroup at , where they were finally defeated after a . Amba Prasad Sufi was killed in this battle. The Ghadarites carried on guerrilla warfare along with the Iranian partisans till 1919.    
Although the conflict in India was not explicitly a part of the First World War, it was part of the wider strategic context. The British attempt to subjugate the rebelling tribal leaders drew away much needed troops from other theaters, in particular, of course, the Western Front, where the real decisive victory would be made.
The reason why some Indian and Afghani tribes rose up simply came down to years of discontent which erupted, probably not coincidentally, during the First World War. It is likely that the tribal leaders were aware that Britain would not be able to field the required men, in terms of either number or quality, but underestimated the strategic importance of India to the British. Despite being far from the epicenter of the conflict, India provided a bounty of men for the fronts. Its produce was also needed for the British war effort and many trade routes running to other profitable areas of the Empire ran through India. Therefore, although the British were not able to send the men that they wanted, they were able to send enough to mount a gradual but effective counter-guerrilla war against the tribesmen. The fighting continued into 1919 and in some areas lasted even longer.
- See also: and
|This section does not any .|
Please help by adding citations to . material may be challenged and removed. (December 2008)
- Main article: Eastern Front (World War I)
While the Western Front had reached stalemate, the war continued in East Europe. Initial Russian plans called for simultaneous invasions of Austrian and German East Prussia. Although Russia's initial advance into Galicia was largely successful, they were driven back from East Prussia by and at and the in August and September 1914. Russia's less developed industrial base and ineffective military leadership was instrumental in the events that unfolded. By the spring of 1915, the Russians had retreated into Galicia, and in May the Central Powers achieved a remarkable breakthrough on 's southern frontiers. On 5 August they captured and forced the Russians to withdraw from Poland. This became known as the "Great Retreat" in Russia and the "Great Advance" in Germany.
- Further information:
- Main article: Russian Revolution of 1917
Dissatisfaction with the Russian government's conduct of the war grew, despite the success of the June 1916 in eastern . The success was undermined by the reluctance of other generals to commit their forces to support the victory. Allied and Russian forces were revived only temporarily with 's entry into the war on 27 August. German forces came to the aid of embattled Austrian units in and fell to the Central Powers on 6 December. Meanwhile, unrest grew in Russia, as the remained at the front. increasingly incompetent rule drew protests and resulted in the murder of her favourite, , at the end of 1916. In March 1917, demonstrations in culminated in the abdication of and the appointment of a weak which shared power with the socialists. This arrangement led to confusion and chaos both at the front and at home. The army became increasingly ineffective.
The war and the government became more and more unpopular. Discontent led to a rise in popularity of the , led by . He promised to pull Russia out of the war and was able to gain power. The in November was followed in December by an armistice and negotiations with Germany. At first the Bolsheviks refused the German terms, but when Germany resumed the war and marched across with impunity, the new government acceded to the on 3 March 1918. It took Russia out of the war and ceded vast territories, including , the , parts of and to the Central Powers. The manpower required for German occupation of former Russian territory may have contributed to the failure of the Spring Offensive, however, and secured relatively little food or other war materiel.
With the Bolsheviks' accession to the Treaty of Brest-Litovsk, the Entente no longer existed. The Allied powers led a small-scale invasion of Russia to stop Germany from exploiting Russian resources and, to a lesser extent, to support the Whites in the . Allied troops landed in and in .
- Further information:
Events of 1917 proved decisive in ending the war, although their effects were not fully felt until 1918. The British naval blockade began to have a serious impact on Germany. In response, in February 1917, the convinced to declare unrestricted submarine warfare, with the goal of starving Britain out of the war. Tonnage sunk rose above 500,000 tons per month from February to July. It peaked at 860,000 tons in April. After July, the reintroduced system became extremely effective in neutralizing the threat. Britain was safe from starvation and German industrial output fell.
The victory of Austria-Hungary and Germany at the led the Allies at the to form the to coordinate planning. Previously, British and French armies had operated under separate commands.
In December, the Central Powers signed an armistice with Russia. This released troops for use in the west. Ironically, German troop transfers could have been greater if their territorial acquisitions had not been so dramatic. With German reinforcements and new American troops pouring in, the final outcome was to be decided on the Western front. The Central Powers knew that they could not win a protracted war, but they held high hopes for a quick offensive. Furthermore, the leaders of the Central Powers and the Allies became increasingly fearful of social unrest and revolution in Europe. Thus, both sides urgently sought a decisive victory. 
Entry of the United States
The United States originally pursued a policy of , avoiding conflict while trying to broker a peace. This resulted in increased tensions with Berlin and London. When a German U-boat sank the British liner in 1915, with 128 Americans aboard, U.S. President vowed, "America was too proud to fight" and demanded an end to attacks on passenger ships. Germany complied. Wilson unsuccessfully tried to mediate a settlement. He repeatedly warned the U.S. would not tolerate unrestricted submarine warfare, in violation of international law and U.S. ideas of human rights. Wilson was under pressure from former president , who denounced German acts as "piracy".  Wilson's desire to have a seat at negotiations at war's end to advance the also played a significant role.  Wilson's Secretary of State, , resigned in protest of the President's decidedly warmongering diplomacy. Other factors contributing to the U.S. entry into the war include the suspected German sabotage of both in , and the in what is now .
Making the case
In January 1917, after the Navy pressured the Kaiser, Germany resumed unrestricted submarine warfare. Britain's secret Royal Navy group, , had broken the German diplomatic code. They intercepted a proposal from Berlin (the ) to Mexico to join the war as Germany's ally against the United States, should the U.S. join. The proposal suggested, if the U.S. were to enter the war, Mexico should declare war against the United States and enlist Japan as an ally. This would prevent the United States from joining the Allies and deploying troops to Europe, and would give Germany more time for their unrestricted submarine warfare program to strangle Britain's vital war supplies. In return, the Germans would promise Mexico support in reclaiming Texas, New Mexico, and Arizona. 
U.S. declaration of war on Germany
After the British revealed the telegram to the United States, President Wilson, who had won reelection on his keeping the country out of the war, released the captured telegram as a way of building support for U.S. entry into the war. He had previously claimed neutrality, while calling for the arming of U.S. merchant ships delivering munitions to combatant Britain and quietly supporting the British blockading of German ports and mining of international waters, preventing the shipment of food from America and elsewhere to combatant Germany. After submarines sank seven U.S. merchant ships and the publication of the , Wilson called for war on Germany, which the declared on 6 April 1917. 
Crucial to U.S. participation was the massive domestic propaganda campaign executed by the overseen by . The campaign included tens of thousands of government-selected community leaders giving brief carefully scripted pro-war speeches at thousands of public gatherings. Along with other branches of government and private vigilante groups like the , it also included the general repression and harassment of people either opposed to American entry into the war or of German heritage. Other forms of propaganda included , photos, large-print posters (designed by several well-known illustrators of the day, including and ), magazine and newspaper articles, etc.
First active U.S. participation
The United States was never formally a member of the Allies but became a self-styled "Associated Power". The United States had a small army, but it drafted four million men and by summer 1918 was sending 10,000 fresh soldiers to France every day. In 1917, the U.S. Congress gave U.S. citizenship to Puerto Ricans when they were drafted to participate in World War I, as part of the . Germany had miscalculated, believing it would be many more months before they would arrive and that the arrival could be stopped by U-boats.  The sent a battleship group to to join with the , to , and to help guard convoys. Several regiments of were also dispatched to France. The British and French wanted U.S. units used to reinforce their troops already on the battle lines and not waste scarce shipping on bringing over supplies. The U.S. rejected the first proposition and accepted the second. General , (AEF) commander, refused to break up U.S. units to be used as reinforcements for British Empire and French units. As an exception, he did allow combat regiments such as the to be used in French divisions.  AEF doctrine called for the use of frontal assaults, which had long since been discarded by British Empire and French commanders because of the large loss of life. 
German Spring Offensive of 1918
- Main article: Spring Offensive
German General drew up plans ( ) for the 1918 offensive on the Western Front. The Spring Offensive sought to divide the British and French forces with a series of feints and advances. The German leadership hoped to strike a decisive blow before significant U.S. forces arrived. The operation commenced on 21 March 1918 with an attack on British forces near . German forces achieved an unprecedented advance of 60 kilometers (40 miles). 
British and French trenches were penetrated using novel , also named Hutier tactics, after General . Previously, attacks had been characterised by long artillery bombardments and massed assaults.  However, in the Spring Offensive, the German Army used artillery only briefly and infiltrated small groups of infantry at weak points. They attacked command and logistics areas and bypassed points of serious resistance. More heavily armed infantry then destroyed these isolated positions. German success relied greatly on the element of surprise. 
The front moved to within 120 kilometers (75 mi) of . Three heavy fired 183 shells on the capital, causing many Parisians to flee. The initial offensive was so successful that Kaiser Wilhelm II declared 24 March a . Many Germans thought victory was near. After heavy fighting, however, the offensive was halted. Lacking tanks or , the Germans were unable to consolidate their gains. The sudden stop was also a result of the four AIF (Australian Imperial Forces) divisions that were "rushed" down, thus doing what no other army had done and stopping the German advance in its tracks. During that time the first Australian division was hurriedly sent north again to stop the second German breakthrough. American divisions, which Pershing had sought to field as an independent force, were assigned to the depleted French and British Empire commands on 28 March. A Supreme War Council of Allied forces was created at the on 5 November 1917.  was appointed as supreme commander of the allied forces. Haig, Petain and Pershing retained tactical control of their respective armies; Foch assumed a coordinating role, rather than a directing role and the British, French and U.S. commands operated largely independently. 
Following Operation Michael, Germany launched against the northern ports. The Allies halted the drive with limited territorial gains for Germany. The German Army to the south then conducted , broadly towards Paris. Operation Marne was launched on 15 July, attempting to encircle and beginning the . The resulting Allied counterattack marked their first successful offensive of the war.
By 20 July the Germans were back at their Kaiserschlacht starting lines,  having achieved nothing. Following this last phase of the war in the West, the German Army never again regained the initiative. German casualties between March and April 1918 were 270,000, including many highly trained stormtroopers.
Meanwhile, Germany was falling apart at home. marches become frequent and morale in the army fell. Industrial output was 53% of 1913 levels.
New states under war zone
In 1918, the internationally recognized and bordering the Ottoman Empire were established, as well as the unrecognized and .
In 1918, the of the declared the (DRA) through the (unified form of ) after the dissolution of the . became the first Commander-in-chief of the DRA. Enver Pasha ordered the creation of a new army to be named the . He ordered the Army of Islam into the DRA, with the goal of taking on the . This new offensive was strongly opposed by the . In early May 1918, the Ottoman army attacked the newly declared DRA. Although the Armenians managed to inflict one defeat on the Ottomans at the , the Ottoman army won a later battle and scattered the Armenian army. The Republic of Armenia was forced to sign the in June 1918.
Allied victory: summer and autumn 1918
- Main articles: Hundred Days Offensive and Weimar Republic
The Allied counteroffensive, known as the , began on 8 August 1918. The developed with III Corps on the left, the on the right, and the and spearheading the offensive in the centre through .   It involved 414 of the and type, and 120,000 men. They advanced 12 kilometers (7 miles) into German-held territory in just seven hours. referred to this day as the "Black Day of the German army".  
The Australian-Canadian spearhead at Amiens, a battle that was the beginning of Germany’s downfall,  helped pull the British armies to the north and the French armies to the south forward. While German resistance on the front at Amiens stiffened, after an advance as far as 14 miles (23 km) and brought the battle there to an end, the French Third Army lengthened the Amiens front on 10 August, when it was thrown in on the right of the , and advanced 4 miles (6 km) liberating Lassigny in fighting which lasted until the 16th. South of the French Third Army General Mangin (The Butcher) drove his French Tenth Army forward at Soissons on 20 August to capture eight thousand prisoners, two hundred guns and the Aisne heights overlooking and menacing the German position north of the Vesle.  Another "Black day" as described by .
Meanwhile General Byng of the Third British Army, reporting that the enemy on his front was thinning in a limited withdrawal, was ordered to attack with 200 tanks toward Bapaume, opening what is known as the Battle of Albert with the specific orders of "To break the enemy's front, in order to outflank the enemies present battle front" (opposite the British Fourth Army at Amiens).  Allied leaders had now realized that to continue an attack after resistance had hardened was a waste of lives and it was better to turn a line than to try and roll over it. Attacks were being undertaken in quick order to take advantage of the successful advances on the flanks and then broken off when that attack lost its initial impetus. 
The British Third Army's 15-mile (24 km) front north of Albert progressed after stalling for a day against the main resistance line to which the enemy had withdrawn.  Rawlinson’s was able to battle its left flank forward between Albert and the Somme straightening the line between the advanced positions of the Third Army and the Amiens front which resulted in recapturing Albert at the same time.  On 26 August the British First Army on the left of the Third Army was drawn into the battle extending it northward to beyond Arras. The Canadian Corps already being back in the vanguard of the fought their way from Arras eastward 5 miles (8 km) astride the heavily defended Arras-Cambrai before reaching the outer defenses of the Hindenburg line, breaching them on the 28th and 29th. Bapaume fell on the 29th to the New Zealand Division of the Third Army and the Australians, still leading the advance of the Fourth Army, were again able to push forward at Amiens to take Peronne and Mont St. Quentin on August 31. Further south the French First and Third Armies had slowly fought forward while the Tenth Army, who had by now crossed the Ailette and was east of the Chemin des Dames, was now near to the Alberich position of the .  During the last week of August the pressure along a 70-mile (113 km) front against the enemy was heavy and unrelenting. From German accounts, "Each day was spent in bloody fighting against an ever and again on-storming enemy, and nights passed without sleep in retirements to new lines."  Even to the north in the British Second and Fifth Armies during August and September were able to make progress taking prisoners and positions that were previously denied them.  On 2 September the outflanking of the , with the breaching of the Wotan Position, made it possible for the Third Army to advance and sent repercussions all along the Western Front. That same day had no choice but to issue orders to six armies for withdrawal back into the Hindenburg line in the south, behind the on the Canadian-First Army's front and back to a line east of the Lys in the north, giving up without a fight the salient seized in the previous April.  According to “We had to admit the necessity…to withdraw the entire front from the Scarpe to the Vesle.” 
In nearly four weeks of fighting since 8 August over 100,000 German prisoners were taken, 75,000 by the BEF and the rest by the French. Since "The Black Day of the German Army" the German High Command realized the war was lost and made attempts for a satisfactory end. The day after the battle Ludenforff told Colonel Mertz "We cannot win the war any more, but we must not lose it either." On 11 August he offered his resignation to the Kaiser, who refused it and replied, "I see that we must strike a balance. We have nearly reached the limit of our powers of resistance. The war must be ended." On 13 August at Spa, Hindenburg, Ludendorff, Chancellor and Foreign minister Hintz agreed that the war could not be ended militarily and on the following day the German Crown Council decided victory in the field was now most improbable. Austria and Hungary warned that they could only continue the war until December and Ludendorff recommended immediate peace negotiations, to which the Kaiser responded by instructing Hintz to seek the Queen of Holland's mediation. Prince Rupprecht warned Prince Max of Baden "Our military situation has deteriorated so rapidly that I no longer believe we can hold out over the winter; it is even possible that a catastrophe will come earlier." On 10 September Hindenburg urged peace moves to Emperor Charles of Austria and Germany appealed to Holland for mediation. On the 14th Austria sent a note to all belligerents and neutrals suggesting a meeting for peace talks on neutral soil and on 15 September Germany made a peace offer to Belgium. Both peace offers were rejected and on 24 September OHL informed the leaders in Berlin that armistice talks were inevitable. 
September saw the Germans continuing to fight strong rear guard actions and launching numerous counter attacks on lost positions, with only a few succeeding and then only temporarily. Contested towns, villages, heights and trenches in the screening positions and outposts of the Hindenburg Line continued to fall to the Allies as well as thousands of prisoners, with the BEF alone taking 30,441 in the last week of September. Further small advances eastward would follow the Third Army victory at Ivincourt on 12 September, the Fourth Armies at Epheny on the 18th and the French gain of Essigny Le Grand a day later. On the 24th a final assault by both the British and French on a four mile (6 km) front would come within two miles (3 km) of St. Quentin.  With the outposts and preliminary defensive lines of the Siegfried and Alberich Positions eliminated the Germans were now completely back in the Hindenburg line. With the Wotan position of that line already breached and the Siegfried position in danger of being turned from the north the time had now come for an assault on the whole length of the line.
The Allied began on 26 September. 260,000 U.S. soldiers went "over the top". All initial objectives were captured; the , which met stiff resistance at , took an extra day to capture its objective. The U.S. Army stalled due to supply problems because its inexperienced headquarters had to cope with large units and a difficult landscape.  At the same time, French units broke through in and closed on the Belgian frontier.  The most significant advance came from Commonwealth units, as they entered Belgium.  The last Belgian town to be liberated before the armistice was Ghent, which the Germans held as a pivot until Allied artillery was brought up.   The German army had to shorten its front and use the Dutch frontier as an anchor to fight rear-guard actions.
By October, it was evident that Germany could no longer mount a successful defence.  They were increasingly outnumbered, with few new recruits. Rations were cut. Ludendorff decided, on 1 October,  that Germany had two ways out — total annihilation or an armistice. He recommended the latter at a summit of senior German officials. Allied pressure did not let up.
Meanwhile, news of Germany's impending military defeat spread throughout the German armed forces. The threat of was rife. Admiral and Ludendorff decided to launch a last attempt to restore the "valour" of the German Navy. Knowing the government of would veto any such action, Ludendorff decided not to inform him. Nonetheless, word of the impending assault reached sailors at . Many rebelled and were arrested, refusing to be part of a naval offensive which they believed to be suicidal. Ludendorff took the blame—the Kaiser dismissed him on 26 October. The collapse of the Balkans meant that Germany was about to lose its main supplies of oil and food. The reserves had been used up, but U.S. troops kept arriving at the rate of 10,000 per day. 
Having suffered over 6 million casualties, Germany moved toward peace. took charge of a new government as to negotiate with the Allies. Negotiations with President Wilson began immediately, in the vain hope that better terms would be offered than with the British and French. Instead Wilson demanded the abdication of the Kaiser. There was no resistance when the on 9 November declared Germany to be a republic. Imperial Germany was dead; a new Germany had been born: the . 
Allied superiority and the stab-in-the-back legend, November 1918
In November 1918 the Allies had ample supplies of men and materiel; continuation of the war would have meant the invasion of Germany. This had unforeseeable consequences; some Allied decision-makers felt the war should be "finished," not just stopped, and many voices on both sides voiced the opinion that the war was not really over.  But most Allied decision-makers were eager to see the end of hostilities.
Berlin was almost 900 miles (1,400 km) from the Western Front; no Allied soldier had ever set foot on German soil in anger, and the Kaiser's armies retreated from the battlefield in good order. Thus many Germans, including , were convinced their armies had not really been defeated, resulting in the .
End of war
The collapse of the Central Powers came swiftly. Bulgaria was the first to sign an armistice on 29 September 1918 at .  On 30 October the capitulated at . 
On 24 October the Italians began a push which rapidly recovered territory lost after the . This culminated in the , which marked the end of the Austro-Hungarian Army as an effective fighting force. The offensive also triggered the disintegration of Austro-Hungarian Empire. During the last week of October declarations of independence were made in Budapest, Prague and Zagreb. On 29 October, the imperial authorities asked Italy for an armistice. But the Italians continued advancing, reaching Trento, Udine and Trieste. On 3 November Austria-Hungary sent a to ask for an . The terms, arranged by telegraph with the Allied Authorities in Paris, were communicated to the Austrian Commander and accepted. The was signed in the Villa Giusti, near , on 3 November. Austria and Hungary signed separate armistices following the overthrow of the .
Following the outbreak of the , a republic was proclaimed on 9 November. The fled to the Netherlands. On 11 November was signed in a railroad carriage at . At 11 a.m. on 11 November 1918 — the eleventh hour of the eleventh day of the eleventh month — a ceasefire came into effect. Opposing armies on the Western Front began to withdraw from their positions. Canadian is traditionally regarded as the last soldier killed in the Great War: he was shot by a German sniper and died at 10:58. 
A formal state of war between the two sides persisted for another seven months, until signing of the with Germany on 28 June 1919. Later treaties with Austria, Hungary, Bulgaria and the Ottoman Empire were signed. However, the latter treaty with the Ottoman Empire was followed by strife (the ) and a final peace treaty was signed between the Allied Powers and the country that would shortly become the , at on 24 July 1923.
Some date the end of the war as being when the Versailles treaty was signed in 1919; by contrast, most commemorations of the war's end concentrate on the armistice of 11 November 1918. Legally the last formal peace treaties were not signed until the Treaty of Lausanne. Under its terms, the Allied forces abandoned on 23 August 1923.
- See also:
The First World War began as a clash of 20th century and 19th century , with inevitably large casualties. By the end of 1917, however, the major armies, now numbering millions of men, had modernised and were making use of , , , , and . Infantry formations were reorganised, so that 100-man companies were no longer the main unit of maneuver. Instead, squads of 10 or so men, under the command of a junior NCO, were favoured. Artillery also underwent a revolution.
In 1914, cannons were positioned in the front line and fired directly at their targets. By 1917, with guns (as well as mortars and even machine guns) was commonplace, using new techniques for spotting and ranging, notably aircraft and (often overlooked) field telephone. missions became commonplace, also, and sound detection was used to locate enemy batteries. Germany was far ahead of the Allies in utilizing heavy indirect fire. She employed 150 and 210 mm in 1914 when the typical French and British guns were only 75 and 105 mm. The British had a 6 (152 mm) howitzer, but it was so heavy it had to be assembled for firing. Germans also fielded Austrian 305 mm and 420 mm guns, and already by the beginning of the war had inventories of various calibers of Minenwerfer ideally suited for trench warfare. 
Much of the combat involved , where hundreds often died for each yard gained. Many of the deadliest battles in history occurred during the First World War. Such battles include , the , , the , , and . The of was employed to provide the German forces with a constant supply of gunpowder, in the face of British naval blockade. Artillery was responsible for the largest number of casualties and consumed vast quantities of explosives. The large number of head-wounds caused by exploding shells and forced the combatant nations to develop the modern steel , led by the French, who introduced the in 1915. It was quickly followed by the , worn by British Imperial and U.S. troops, and in 1916 by the distinctive German Stahlhelm, a design, with improvements, still in use today. There was and small-scale , both of which were outlawed by the 1907 Hague Conventions, and both proving of limited effectiveness,  though they captured the public imagination. 
The widespread use of chemical warfare was a distinguishing feature of the conflict. Gases used included , and . Only a small proportion of total war casualties were caused by gas. Effective countermeasures to gas attacks were quickly created, such as .
The most powerful land-based weapons were weighing hundreds of tons apiece. These were nicknamed , even though the namesake was not a railway gun. Germany developed the , able to bombard Paris from over 100 km (60 mi), though shells were relatively light at 94 kilograms (210 lb). While the Allies had railway guns, German models severely out-ranged and out-classed them. were first used militarily by the Italians in Libya 23 October 1911 during the for reconnaissance, soon followed by the dropping of grenades and the next year. By 1914 the military utility was obvious. They were initially used for and . To shoot down enemy planes, anti-aircraft guns and were developed. were created, principally by the Germans and British, though the former used as well.
Towards the end of the conflict, were used for the first time, with launching in a raid against the Zeppelin hangars at in 1918. German () were deployed after the war began. Alternating between restricted and unrestricted submarine warfare in the Atlantic, they were employed by the in a strategy to deprive the of vital supplies. The deaths of British merchant sailors and the seeming invulnerability of U-boats led to the development of (1916), (passive , 1917), , submarines (, 1917), forward-throwing , and dipping hydrophones (the latter two both abandoned in 1918).  To extend their operations, the Germans proposed supply submarines (1916). Most of these would be forgotten in the until World War II revived the need.
Trenches, machineguns, air reconnaissance, barbed wire, and modern artillery with fragmentation helped bring the battle lines of World War I to a stalemate. The British sought a solution with the creation of the tank and . The were used during the on 15 September 1916. Mechanical reliability became an issue, but the experiment proved its worth. Within a year, the British were fielding tanks by the hundreds and showed their potential during the in November 1917, by breaking the Hindenburg Line, while teams captured 8000 enemy soldiers and 100 guns. Light also were introduced, such as the and .
Manned , floating high above the trenches, were used as stationary reconnaissance platforms, reporting enemy movements and directing artillery. Balloons commonly had a crew of two, equipped with .  In the event of an enemy air attack, the crew could parachute to safety. At the time, parachutes were too heavy to be used by pilots of aircraft (with their marginal power output) and smaller versions would not be developed until the end of the war; they were also opposed by British leadership, who feared they might promote cowardice.  Recognised for their value as observation platforms, balloons were important targets of enemy aircraft. To defend against air attack, they were heavily protected by antiaircraft guns and patrolled by friendly aircraft; to attack them, unusual weapons such as air-to-air rockets were even tried. Blimps and balloons contributed to air-to-air combat among aircraft, because of their reconnaissance value, and to the trench stalemate, because it was impossible to move large numbers of troops undetected. The Germans conducted air raids on England during 1915 and 1916 with airships, hoping to damage British morale and cause aircraft to be diverted from the front lines. The resulting panic took several squadrons of fighters from France.  Another new weapon, , were first used by the German army and later adopted by other forces. Although not of high tactical value, they were a powerful, demoralizing weapon and caused terror on the battlefield. It was a dangerous weapon to wield, as its heavy weight made operators vulnerable targets.
evolved to supply the enormous quantities of food, water, and ammunition required to support large numbers of soldiers in areas where conventional transportation systems had been destroyed. A trench railway system was included in construction of the , but internal combustion engines and improved traction systems for wheeled vehicles rendered trench railways obsolete within a decade.
Trying to comprehend
- Main article: World War I in art and literature
- Main article: Media of World War I
- Main article: War memorials
The first tentative efforts to comprehend the meaning and consequences of modern warfare began during the initial phases of the war, and this process continued throughout and after the end of hostilities.
- Main article: Surviving veterans of World War I
- Main article: World War I casualties
- Main article: Commonwealth War Graves Commission
- Main article: American Battle Monuments Commission
The soldiers of the war were initially volunteers, except for , but increasingly were into service. Books such as All Quiet on the Western Front detail the mundane time, but also the intense horror, of soldiers that fought the war. Britain's has collected more than 2,500 recordings of soldiers' personal accounts and selected transcripts, edited by military author , have been published. The museum believes that historians have not taken full account of this material and accordingly has made the full archive of recordings available to authors and researchers. 
Some became casualties of war -- "the honored dead" -- and some survived to be called "veterans."
Prisoners of war
About 8 million men surrendered and were held in during the war. All nations pledged to follow the Hague Convention on fair treatment of . In general, a POW's rate of survival was much higher than their peers at the front.  Individual surrenders were uncommon. Large units usually surrendered en masse. At the 92,000 Russians surrendered. When the besieged garrison of surrendered in 1915, 20,000 Russians became prisoners. Over half of Russian losses were prisoners (as a proportion of those captured, wounded or killed); for Austria 32%, for Italy 26%, for France 12%, for Germany 9%; for Britain 7%. Prisoners from the Allied armies totalled about 1.4 million (not including Russia, which lost between 2.5 and 3.5 million men as prisoners.) From the Central Powers about 3.3 million men became prisoners. 
Germany held 2.5 million prisoners; Russia held 2.9 million and Britain and France held about 720,000. Most were captured just prior to the Armistice. The U.S. held 48,000. The most dangerous moment was the act of surrender, when helpless soldiers were sometimes gunned down.   Once prisoners reached a camp, in general, conditions were satisfactory (and much better than in World War II), thanks in part to the efforts of the and inspections by neutral nations. Conditions were terrible in Russia, was common for prisoners and civilians alike; about 15–20% of the prisoners in Russia died. In Germany food was in short supply, but only 5% died.   
The Ottoman Empire often treated POWs poorly.  Some 11,800 British Empire soldiers, most of them Indians, became prisoners after the , in , in April 1916; 4,250 died in captivity.  Although many were in very bad condition when captured, Ottoman officers forced them to march 1,100 kilometres (684 mi) to . A survivor said: "we were driven along like beasts, to drop out was to die."  The survivors were then forced to build a railway through the .
In Russia, where the prisoners from the of the Austro-Hungarian army were released in 1917 they re-armed themselves and briefly became a military and diplomatic force during the Russian Civil War.
Military attachés and war correspondents
- Main article: Military attachés and war correspondents in the First World War
Military and civilian observers from every major power closely followed the course of the war. Many were able to report on events from a perspective somewhat like what is now termed "" positions within the opposing land and naval forces. These military attachés and other observers prepared voluminous first-hand accounts of the war and analytical papers.
For example, former U.S. Army Captain followed the developments of the from an embedded perspective within the ranks of the Turkish defenders; and his report was passed through Turkish censors before being printed in London and New York.  However, this observer's role was abandoned when the U.S. entered the war, as Fortescue immediately re-enlisted, sustaining wounds at in the , September 1918. 
In-depth observer narratives of the war and more narrowly focused professional journal articles were written soon after the war; and these post-war reports conclusively illustrated the battlefield destructiveness of this conflict. This was the not first time the tactics of entrenched positions for infantry defended with machine guns and artillery became vitally important. The had been closely observed by Military attachés, war correspondents and other observers; but, from a 21st Century perspective, it is now apparent that a range of tactical lessons were disregarded or not used in the preparations for war in and during the course of the Great War. 
An early recorded use of the term "World War" is attributed to a well-known journalist for , Colonel , who wrote in his diary on 10 September 1918: "We discussed the right name of the war. I said the we called it now The War, but that this could not last. The Napoleonic War was The Great War. To call it The German War was too much flattery for the Boche. I suggested The World War as a shade better title, and finally we mutually agreed to call it The First World War in order to prevent the millennium folk from forgetting that the history of the world was the history of war." 
Opposition to the war
- Main articles: Opposition to World War I and French Army Mutinies (1917)
The and movements had long voiced their opposition to a war, which they argued, meant only that workers would kill other workers in the interest of . Once war was declared, however, many socialists and trade unions backed their governments. Among the exceptions were the , the , and the , and individuals such as , and their followers in Germany. There were also small anti-war groups in Britain and France. Other opposition came from - some socialist, some religious - who refused to fight. In Britain 16,000 people asked for conscientious objector status.  Many suffered years of prison, including and bread and water diets. Even after the war, in Britain many job advertisements were marked "No conscientious objectors need apply". Many countries jailed those who spoke out against the conflict. These included in the United States and in Britain. In the U.S. the 1917 effectively made free speech illegal and many served long prison sentences for statements of fact deemed unpatriotic. The made any statements deemed "disloyal" a federal crime. Publications at all critical of the government were removed from circulation by postal censors. 
- Main article: Ottoman casualties of World War I
- See also: , , and
The of the Ottoman Empire's population, with the most prominent among them being the massacres of (similar policies were enacted against the and ), during the final years of the Ottoman Empire is considered by some .  The Ottomans saw the entire Armenian population as an  that had chosen to side with Russia during the beginning of the war.  The exact number of deaths is unknown although a range of 250,000 to 1.5 million is given for the deaths of Armenians.  The government of Turkey has consistently charges of genocide and of others, arguing that those who died were simply caught up in the fighting or that killings of Armenians and other Christians were justified by their individual or collective . 
Rape of Belgium
- Main article: Rape of Belgium
In Belgium, German troops, in fear of French and Belgian guerrilla fighters, or francs-tireurs, massacred townspeople in (211 dead), (384 dead), and (612 dead). On 25 August 1914, the Germans set fire to the town of , burned the library containing about 230,000 books, killed 209 civilians and forced 42,000 to evacuate. These actions brought worldwide condemnation. 
- Main article: Aftermath of World War I
No other war had changed the map of Europe so dramatically — four empires disappeared: the German, Austro-Hungarian, Ottoman and the Russian. Four defunct dynasties, the , the , and the together with all their ancillary aristocracies, all fell after the war. Belgium was badly damaged, as was France with 1.4 million soldiers dead, not counting other casualties. Germany and Russia were similarly affected.
Of the 60 million European soldiers who were mobilized from 1914 – 1918, 8 million were killed, 7 million were permanently disabled, and 15 million were seriously injured. Germany lost 15.1% of its active male population, Austria-Hungary lost 17.1%, and France lost 10.5%.  About 750,000 German civilians died from caused by the British blockade during the war.  The war had profound economic consequences. In addition, a that started in in the latter months of the war, killed millions in Europe and then spread around the world. Overall, the killed at least 50 million people.   During the war, typhus epidemics have killed 150,000 in Serbia. There were about 30 million infections and 3 million deaths from in Russia from 1918 to 1922.  By 1922 there were at least 7 million homeless children in Russia as a result of nearly a decade of devastation from World War I and the . 
The end of World War I set the stage for other world conflicts, some of which are continuing into the 21st century. The , led by , pushed for socialist revolution. Out of German discontent with the still controversial , was able to gain popularity and power.   was in part a continuation of the power struggle that was never fully resolved by the First World War; in fact, it was common for Germans in the 1930s and 1940s to justify acts of international aggression because of perceived injustices imposed by the victors of the First World War. 
The birth of and the roots of the continuing are partially found in the unstable power dynamics of the which were born at the end of World War I.  Previous to the end of fighting in the war, the had maintained a modest level of peace and stability throughout the Middle East.  With the end of the war and the fall of Ottoman government, power vacuums developed and conflicting claims to land and nationhood began to emerge.  Sometimes after only cursory consultation with the local population, the political boundaries drawn by the victors of the First World War were quickly imposed, and in many cases are still problematic in the 21st century struggles for .   While the dissolution of the at the end of World War I was a pivotal milestone in the creation of the modern political situation of the Middle East, including especially the ,    the end of Ottoman rule also spawned lesser known disputes over water and other natural resources. 
- Further information:
After the war, the Allies imposed a series of peace treaties on the Central Powers. The 1919 , which Germany was kept under blockade until she signed, ended the war. It declared Germany responsible for the war and required Germany to pay enormous and award territory to the victors. Unable to pay them with exports (a result of territorial losses and postwar recession),  she did so by borrowing from the United States, until the reparations were suspended in 1931. The "Guilt Thesis" became a controversial explanation of events in Britain and the United States. The Treaty of Versailles caused enormous bitterness in Germany, which nationalist movements, especially the , exploited with a they called the . The treaty contributed to economic collapse of the by sparking runaway inflation in the 1920s.
The German Empire lost its and was saddled with accepting blame for the war, as well as paying punitive for it. The Austro-Hungarian and Ottoman empires were completely dissolved.
Austria-Hungary was also partitioned, largely along ethnic lines, into several successor states including , , , and , as well as adding to the who was allied with the victors. . The details were contained in the and the .
The Russian Empire, which had withdrawn from the war in 1917 after the , lost much of its western frontier as the newly independent nations of , , , , and were carved from it; was also re-attached to the as it had been a Romanian territory for more than a thousand years. 
The Ottoman Empire disintegrated, and much of its non- territory was awarded as protectorates of various Allied powers, while the remaining Turkish core was reorganised as the . The Ottoman Empire was to be partitioned by the in 1920. The treaty, however, was never ratified by the Sultan and was rejected by the . This led to the and, ultimately, to the 1923 .
New national identities
|This section needs additional for .|
Please help by adding . Unsourced material may be and removed. (May 2008)
reemerged as an independent country, after more than a century. and were entirely new nations agglomerating previously independent peoples. Russia became the and lost , , and , which became independent countries. The Ottoman Empire was soon replaced by and several other countries in the Middle East.
In the British Empire, the war unleashed new forms of nationalism. In and the became known as those nations' "Baptism of Fire". It was the first major war in which the newly established countries fought and it was one of the first times that Australian troops fought as Australians, not just subjects of the . , commemorating the , celebrates this defining moment.  
After the , where the Canadian divisions fought together for the first time as a single corps, Canadians began to refer to theirs as a nation "forged from fire".  Having succeeded on the same battleground where the "mother countries" had previously faltered, they were for the first time respected internationally for their own accomplishments. Having entered the war as a Dominion of the British Empire, by its end Canada emerged as a fully independent nation.   While the other Dominions were represented by Britain, Canada was an independent negotiator and signatory of the .
|This section needs additional for . Please help by adding . Unsourced material may be and removed. (January 2008)|
The experiences of the war led to a collective trauma for all participating countries. The of the 1900s was gone and those who fought in the war became known as the . For the next few years, much of Europe mourned. Memorials were erected in thousands of villages and towns. The soldiers returning home from World War I suffered greatly from the horrors they had witnessed. Many returning veterans suffered from , called at the time.
The social trauma caused by years of fighting manifested itself in different ways. Some people were revolted by and its results, and so they began to work toward a more world, supporting organisations such as the . became increasingly popular. Others had the opposite reaction, feeling that only strength and military might could be relied upon in a chaotic and inhumane world. views were an outgrowth of the many changes taking place in society. The rise of and included a revival of the nationalist spirit and a rejection of many post-war changes. Similarly, the popularity of the ("stab-in-the-back legend") was a testament to the of defeated Germany and was a rejection of responsibility for the conflict. The of betrayal became common and the German public came to see themselves as victims. The Dolchstosslegende's popular acceptance in Germany played a significant role in the rise of Nazism. A sense of disillusionment and became pronounced, with growing in popularity. This disillusionment for humanity found a cultural climax with the . Many believed the war heralded the end of the world as they had known it, including the collapse of and . and movements around the world drew strength from this theory and enjoyed a level of popularity they had never known before. These feelings were most pronounced in areas directly or harshly affected by the war.   On 3 May 1915, during the , Lieutenant Alexis Helmer was killed. At his graveside, his friend , M.D., of , , Canada wrote the memorable poem In Flanders Fields as a salute to those who perished in the Great War. Published in on 8 December 1915, it is still recited today, especially on and .  
Macro- and micro-economic effects
One of the most dramatic effects of the war was the expansion of governmental powers and responsibilities in Britain, France, the United States, and the of the British Empire. In order to harness all the power of their societies, new government ministries and powers were created. New taxes were levied and laws enacted, all designed to bolster the ; many of which have lasted to this day. Similarly, the war strained the abilities of the formerly large and bureaucratised governments such as in Austria-Hungary and Germany; however, any analysis of the long-term effects were clouded by the defeat of these governments.
(GDP) increased for three Allies (Britain, Italy, and U.S.), but decreased in France and Russia, in neutral Netherlands, and in the main three Central Powers. The shrinkage in GDP in Austria, Russia, France, and the Ottoman Empire reached 30 to 40%. In Austria, for example, most of the pigs were slaughtered and, at war's end, there was no meat.
All nations had increases in the government's share of GDP, surpassing fifty percent in both Germany and France and nearly reaching fifty percent in Britain. To pay for purchases in the United States, Britain cashed in its massive investments in American railroads and then began borrowing heavily on . President Wilson was on the verge of cutting off the loans in late 1916, but allowed a massive increase in lending to the Allies. After 1919, the U.S. demanded repayment of these loans, which, in part, were funded by German reparations, which, in turn, were supported by American loans to Germany. This circular system collapsed in 1931 and the loans were never repaid.
Macro- and micro-economic consequences devolved from the war. Families were altered by the departure of many men. With the death or absence of the primary wage earner, women were forced into the workforce in unprecedented numbers. At the same time, industry needed to replace the lost laborers sent to war. This aided the struggle for .
As the war slowly turned into a , was implemented in some countries. This issue was particularly explosive in Canada and Australia. In the former it opened a political gap between French-Canadians — who claimed their true loyalty was to Canada and not the British Empire — and the majority who saw the war as a duty to both Britain and Canada. Prime Minister pushed through a , provoking the . In Australia, a sustained pro-conscription campaign by Prime Minister , caused a split in the and Hughes formed the in 1917 to pursue the matter. Nevertheless, the , the , and expatriates successfully opposed Hughes' push, which was .
In Britain, rationing was finally imposed in early 1918, limited to meat, sugar, and fats (butter and ), but not bread. The new system worked smoothly. From 1914 to 1918 trade union membership doubled, from a little over four million to a little over eight million. Work stoppages and strikes became frequent in 1917–18 as the unions expressed grievances regarding prices, alcohol control, pay disputes, fatigue from overtime and working on Sundays and inadequate housing. Conscription put into uniform nearly every physically fit man, six of ten million eligible. Of these, about 750,000 lost their lives and 1,700,000 were wounded. Most deaths were to young unmarried men; however, 160,000 wives lost husbands and 300,000 children lost fathers. 
Britain turned to her colonies for help in obtaining essential war materials whose supply had become difficult from traditional sources. Geologists, such as , were called upon to find new resources of precious minerals in the African colonies. Kitson discovered important new deposits of , used in munitions production, in the . 
Cognate names for the war
Before World War II, the war was also known as The Great War, The World War, The War to End All Wars, The Kaiser's War, The War of the Nations and The War in Europe. In France and Belgium it was sometimes referred to as La Guerre du Droit (the War for Justice) or La Guerre Pour la Civilisation / de Oorlog tot de Beschaving (the War to Preserve Civilization), especially on medals and commemorative monuments.
The term used by official histories of the war in Britain and Canada is The First World War, while American histories generally use the term World War I.
There is evidence that German biologist and philosopher used the key phrase shortly after the start of the fighting in Europe: "There is no doubt that the course and character of the feared "European War"...will become the first world war the full sense of the word." 
Although the widespread use of the term First World War has been dated to 1931, the first known appearance of the phrase in print was in the 's issue for 20 September 1914. 
In many European countries, it appears the current usage is tending back to calling it The Great War / la Grande Guerre / de Grote Oorlog / der Große Krieg, because of the growing historical awareness that, of the two 20th century world wars, the 1914–1918 conflict caused more social, economic and political upheaval.  It was also one of the prime factors in the outbreak of the Second World War.