World War I Clockwise from top: trenches on the Western Front; a British Mark IV Tank crossing a trench; Royal Navy battleship HMS Irresistible sinking after striking a mine at the Battle of the Dardanelles; a Vickers machine gun crew with gas masks, and German Albatros D.III biplanes Date 28 July 1914 – 11 November 1918 (Armistice) Treaty of Versailles signed 28 June 1919 Treaty of Saint-Germain-en-Laye signed 10 September 1919 Treaty of Neuilly-sur-Seine signed 27 November 1919 Treaty of Trianon signed 4 June 1920 Treaty of Sèvres signed 10 August 1920 Location Europe, Africa, the Middle East, the Pacific Islands, China and off the coast of South and North America Result Allied victory End of the German, Russian, Ottoman, and Austro-Hungarian empires Formation of new countries in Europe and the Middle East Transfer of German colonies and regions of the former Ottoman Empire to other powers Establishment of the League of Nations. (more...) Belligerents Allied (Entente) Powers French Third Republic British Empire  Russia (1914–17)  Italy (1915–18)  United States (1917–18)  Romania (1916–18) Empire of Japan Kingdom of Serbia  Belgium  Greece (1917–18) and others Central Powers German Empire  Austria-Hungary  Ottoman Empire  Bulgaria (1915–18) Commanders and leaders Leaders and commanders Raymond Poincaré Georges Clemenceau Ferdinand Foch H. H. Asquith David Lloyd George Douglas Haig Nicholas II Nicholas Nikolaevich Antonio Salandra Vittorio Orlando Luigi Cadorna Woodrow Wilson John J. Pershing Ferdinand I and others Leaders and commanders Wilhelm II Paul von Hindenburg Erich Ludendorff Franz Joseph I Karl I Conrad von Hötzendorf Mehmed V Enver Pasha Mustafa Kemal Ferdinand I Nikola Zhekov and others Strength Entente[1] 12,000,000 8,841,541[2][3] 8,660,000[4] 5,093,140 4,743,826 1,234,000 800,000 707,343 380,000 250,000 Total: 42,959,850 Central Powers[1] 13,250,000 7,800,000 2,998,321 1,200,000 Total: 25,248,321 Casualties and losses Military dead: 5,525,000 Military wounded: 12,831,500 Military missing: 4,121,000 Total: 22,477,500 KIA, WIA or MIA ...further details. Military dead: 4,386,000 Military wounded: 8,388,000 Military missing: 3,629,000 Total: 16,403,000 KIA, WIA or MIA ...further details.

v t e Theatres of World War I European: Balkans Western Front Eastern Front Italian Front Middle Eastern: Caucasus Persia Gallipoli Mesopotamia Sinai and Palestine South Arabia African: South-West Africa West Africa East Africa North Africa Asian and Pacific theatre Other theatres: America Atlantic Ocean Mediterranean

World War I (WWI), which was predominantly called the World War or the Great War from its occurrence until 1939 (World War II), and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918. It involved all the world's great powers,^[5] which were assembled in two opposing alliances: the Allies (based on the Triple Entente of the United Kingdom, France and Russia) and the Central Powers (originally centred around the Triple Alliance of Germany, Austria-Hungary and Italy; but, as Austria–Hungary had taken the offensive against the agreement, Italy did not enter into the war).^[6] These alliances both reorganised (Italy fought for the Allies), and expanded as more nations entered the war. Ultimately more than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history.^[7][8] More than 9 million combatants were killed, largely because of enormous increases in lethality of weapons, thanks to new technology, without corresponding improvements in protection or mobility. It was the sixth-deadliest conflict in world history, subsequently paving the way for various political changes such as revolutions in the nations involved.^[9]

Long-term causes of the war included the imperialistic foreign policies of the great powers of Europe, including the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, the Russian Empire, the British Empire, the French Republic, and Italy. The assassination on 28 June 1914 of Archduke Franz Ferdinand of Austria, the heir to the throne of Austria-Hungary, by a Yugoslav nationalist in Sarajevo, Bosnia and Herzegovina was the proximate trigger of the war. It resulted in a Habsburg ultimatum against the Kingdom of Serbia.^[10][11] Several alliances formed over the previous decades were invoked, so within weeks the major powers were at war; via their colonies, the conflict soon spread around the world.

On 28 July, the conflict opened with the Austro-Hungarian invasion of Serbia,^[12][13] followed by the German invasion of Belgium, Luxembourg and France; and a Russian attack against Germany. After the German march on Paris was brought to a halt, the Western Front settled into a static battle of attrition with a trench line that changed little until 1917. In the East, the Russian army successfully fought against the Austro-Hungarian forces but was forced back from East Prussia and Poland by the German army. Additional fronts opened after the Ottoman Empire joined the war in 1914, Italy and Bulgaria in 1915 and Romania in 1916. The Russian Empire collapsed in March 1917, and Russia left the war after the October Revolution later that year. After a 1918 German offensive along the western front, United States forces entered the trenches and the Allies drove back the German armies in a series of successful offensives. Germany, which had its own trouble with revolutionaries at this point, agreed to a cease-fire on 11 November 1918, later known as Armistice Day. The war had ended in victory for the Allies.

Events on the home fronts were as tumultuous as on the battle fronts, as the participants tried to mobilize their manpower and economic resources to fight a total war. By the end of the war, four major imperial powers — the German, Russian, Austro-Hungarian and Ottoman empires — ceased to exist. The successor states of the former two lost a great amount of territory, while the latter two were dismantled entirely. The map of central Europe was redrawn into several smaller states.^[14] The League of Nations was formed in the hope of preventing another such conflict. The European nationalism spawned by the war and the breakup of empires, the repercussions of Germany's defeat and problems with the Treaty of Versailles are agreed to be factors contributing to World War II.^[15]

Names[link]

In Canada, Maclean's Magazine in October 1914 said, "Some wars name themselves. This is the Great War."^[16] During the Interwar period, the war was most often called the World War and the Great War, in English-speaking countries.

After the onset of the Second World War in 1939, the terms World War I or the First World War became standard, with British and Canadian historians favouring the First World War, and Americans World War I. The notion that the "World War" was merely the first in a series was not a new idea at the time, however; it was first introduced in September 1914 by German philosopher Ernst Haeckel, who claimed that "there is no doubt that the course and character of the feared 'European War' ... will become the first world war in the full sense of the word."^[17] The First World War was the title of a 1920 history by the officer and journalist Charles à Court Repington.

Background[link]

Map of the participants in World War I: Allied Powers in green, Central Powers in orange, and neutral countries in grey

In the 19th century, the major European powers had gone to great lengths to maintain a balance of power throughout Europe, resulting by 1900 in a complex network of political and military alliances throughout the continent.^[6] These had started in 1815, with the Holy Alliance between Prussia, Russia, and Austria. Then, in October 1873, German Chancellor Bismarck negotiated the League of the Three Emperors (German: Dreikaiserbund) between the monarchs of Austria–Hungary, Russia and Germany. This agreement failed because Austria–Hungary and Russia could not agree over Balkan policy, leaving Germany and Austria–Hungary in an alliance formed in 1879, called the Dual Alliance. This was seen as a method of countering Russian influence in the Balkans as the Ottoman Empire continued to weaken.^[6] In 1882, this alliance was expanded to include Italy in what became the Triple Alliance.^[18]

After 1870, European conflict was averted largely through a carefully planned network of treaties between the German Empire and the remainder of Europe orchestrated by Bismarck. He especially worked to hold Russia at Germany's side to avoid a two-front war with France and Russia. When Wilhelm II ascended to the throne as German Emperor (Kaiser), Bismarck's alliances were gradually de-emphasised. For example, the Kaiser refused to renew the Reinsurance Treaty with Russia in 1890. Two years later, the Franco-Russian Alliance was signed to counteract the force of the Triple Alliance. In 1904, the United Kingdom sealed an alliance with France, the Entente Cordiale, and in 1907, the United Kingdom and Russia signed the Anglo-Russian Convention. This system of interlocking bilateral agreements formed the Triple Entente.^[6]

HMS Dreadnought. A naval arms race existed between the United Kingdom and Germany.

German industrial and economic power had grown greatly after unification and the foundation of the Empire in 1871. From the mid-1890s on, the government of Wilhelm II used this base to devote significant economic resources to building up the Kaiserliche Marine (Imperial German Navy), established by Admiral Alfred von Tirpitz, in rivalry with the British Royal Navy for world naval supremacy.^[19] As a result, each nation strove to out-build the other in terms of capital ships. With the launch of HMS Dreadnought in 1906, the British Empire expanded on its significant advantage over its German rival.^[19] The arms race between Britain and Germany eventually extended to the rest of Europe, with all the major powers devoting their industrial base to producing the equipment and weapons necessary for a pan-European conflict.^[20] Between 1908 and 1913, the military spending of the European powers increased by 50 percent.^[21]

Gavrilo Princip, a Bosnian-Serb student, was arrested immediately after he assassinated Archduke Franz Ferdinand of Austria

Austria-Hungary precipitated the Bosnian crisis of 1908–1909 by officially annexing the former Ottoman territory of Bosnia and Herzegovina, which it had occupied since 1878. This angered the Kingdom of Serbia and its patron, the Pan-Slavic and Orthodox Russian Empire.^[22] Russian political manoeuvring in the region destabilised peace accords that were already fracturing in what was known as "the powder keg of Europe".^[22]

Ethno-linguistic map of Austria–Hungary, 1910

In 1912 and 1913 the First Balkan War was fought between the Balkan League and the fracturing Ottoman Empire. The resulting Treaty of London further shrank the Ottoman Empire, creating an independent Albanian State while enlarging the territorial holdings of Bulgaria, Serbia, Montenegro, and Greece. When Bulgaria attacked both Serbia and Greece on 16 June 1913, it lost most of Macedonia to Serbia and Greece and Southern Dobruja to Romania in the 33-day Second Balkan War, further destabilising the region.^[23]

On 28 June 1914, Gavrilo Princip, a Bosnian-Serb student and member of Young Bosnia, assassinated the heir to the Austro-Hungarian throne, Archduke Franz Ferdinand of Austria in Sarajevo, Bosnia.^[24] This began a period of diplomatic manoeuvring among Austria-Hungary, Germany, Russia, France, and Britain called the July Crisis. Wanting to finally end Serbian interference in Bosnia, Austria-Hungary delivered the July Ultimatum to Serbia, a series of ten demands intentionally made unacceptable, intending to provoke a war with Serbia.^[25] When Serbia agreed to only eight of the ten demands, Austria-Hungary declared war on 28 July 1914. Strachan argues, "Whether an equivocal and early response by Serbia would have made any difference to Austria-Hungary's behaviour must be doubtful. Franz Ferdinand was not the sort of personality who commanded popularity, and his demise did not cast the empire into deepest mourning".^[26]

The Russian Empire, unwilling to allow Austria–Hungary to eliminate its influence in the Balkans, and in support of its longtime Serb protégés, ordered a partial mobilisation one day later.^[18] When the German Empire began to mobilise on 30 July 1914, France, resentful of the German conquest of Alsace-Lorraine during the Franco-Prussian War, ordered French mobilisation on 1 August. Germany declared war on Russia on the same day.^[27] The United Kingdom declared war on Germany on 4 August 1914, following an "unsatisfactory reply" to the British ultimatum that Belgium must be kept neutral.^[28]

Theatres of conflict[link]

Opening hostilities[link]

Confusion among the Central Powers[link]

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. Previously tested deployment plans had been replaced early in 1914, but the replacements had never been tested in exercises. Austro-Hungarian leaders believed Germany would cover its northern flank against Russia.^[29] Germany, however, envisioned Austria-Hungary directing most of its troops against Russia, while Germany dealt with France. This confusion forced the Austro-Hungarian Army to divide its forces between the Russian and Serbian fronts.

On 9 September 1914, the Septemberprogramm, a possible plan which detailed Germany's specific war aims and the conditions that Germany sought to force on the Allied Powers, was outlined by German Chancellor Theobald von Bethmann-Hollweg. It was never officially adopted.

African campaigns[link]

Lettow surrendering his forces to the British at Abercorn

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 Togoland. On 10 August, German forces in South-West Africa attacked South Africa; sporadic and fierce fighting continued for the rest of the war. The German colonial forces in German East Africa, led by Colonel Paul Emil von Lettow-Vorbeck, fought a guerrilla warfare campaign during World War I and only surrendered two weeks after the armistice took effect in Europe.^[30]

Serbian campaign[link]

Declaration of war. Austro-Hungarian government's telegram to the government of Serbia on 28 July 1914.

Austria invaded and fought the Serbian army at the Battle of Cer and Battle of Kolubara beginning on 12 August. Over the next two weeks Austrian attacks were thrown back with heavy losses, which marked the first major Allied victories of the war and dashed Austro-Hungarian hopes of a swift victory. As a result, Austria had to keep sizable forces on the Serbian front, weakening its efforts against Russia.^[31] Serbia’s defeat of the Austro-Hungarian invasion of 1914 counts among the major upset victories of the last century.^[32]

German forces in Belgium and France[link]

German soldiers in a railway goods van on the way to the front in 1914. A message on the car spells out "Trip to Paris"; early in the war all sides expected the conflict to be a short one.

At the outbreak of the First World War, the German army (consisting in the West of seven field armies) carried out a modified version of the Schlieffen Plan, designed to quickly attack France through neutral Belgium before turning southwards to encircle the French army on the German border.^[10] The plan called for the right flank of the German advance to converge on Paris, and initially the Germans were successful, particularly in the Battle of the Frontiers (14–24 August). By 12 September, the French, with assistance from the British forces, halted the German advance east of Paris at the First Battle of the Marne (5–12 September). The last days of this battle signified the end of mobile warfare in the west.^[10] The French offensive into Germany, launched on 7 August with the Battle of Mulhouse, had limited success.

In the east, only one field army defended East Prussia, and when Russia attacked in this region it diverted German forces intended for the Western Front. Germany defeated Russia in a series of battles collectively known as the First Battle of Tannenberg (17 August – 2 September), but this diversion aggravated problems of insufficient speed of advance from rail-heads not foreseen by the German General Staff. The Central Powers were 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 early victory.^[33]

Asia and the Pacific[link]

New Zealand occupied German Samoa (later Western Samoa) on 30 August. On 11 September, the Australian Naval and Military Expeditionary Force landed on the island of Neu Pommern (later New Britain), which formed part of German New Guinea. Japan seized Germany's Micronesian colonies and, after the Siege of Tsingtao, the German coaling port of Qingdao in the Chinese Shandong peninsula. Within a few months, the Allied forces had seized all the German territories in the Pacific; only isolated commerce raiders and a few holdouts in New Guinea remained.^[34][35]

Early stages[link]

Trench warfare begins[link]

Sir Winston Churchill with the Royal Scots Fusiliers, 1916

Sunlight Soap ad, placed in a trench (1915)

Military tactics before World War I had failed to keep pace with advances in technology. These advances allowed for impressive defence systems, which out-of-date military tactics could not break through for most of the war. Barbed wire was a significant hindrance to massed infantry advances. Artillery, vastly more lethal than in the 1870s, coupled with machine guns, made crossing open ground extremely difficult.^[36] The Germans introduced poison gas; 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.^{[citation needed]} 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 tank.^[37] Britain and France were its primary users; the Germans employed captured Allied tanks and small numbers of their own design. After the First Battle of the Marne, both Entente and German forces began a series of outflanking manoeuvres, in the so-called "Race to the Sea". Britain and France soon found themselves facing entrenched German forces from Lorraine to Belgium's coast.^[10] Britain and France sought to take the offensive, while Germany defended the occupied territories; consequently, German trenches were much better constructed than those of their enemy. Anglo-French trenches were only intended to be "temporary" before their forces broke through German defences.^[38] Both sides tried to break the stalemate using scientific and technological advances. On 22 April 1915 at the Second Battle of Ypres, the Germans (violating the Hague Convention) used chlorine gas for the first time on the Western Front. Algerian troops retreated when gassed and a six-kilometre (four-mile) hole opened in the Allied lines that the Germans quickly exploited, taking Kitcheners' Wood. Canadian soldiers closed the breach at the Second Battle of Ypres.^[39] At the Third Battle of Ypres, Canadian and ANZAC troops took the village of Passchendaele.

Men in Melbourne collecting recruitment papers

In the trenches: Royal Irish Rifles in a communications trench on the first day on the Somme, 1 July 1916.

On 1 July 1916, the British Army endured the bloodiest day in its history, suffering 57,470 casualties, including 19,240 dead, on the first day of the Battle of the Somme. 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.^[40]

Neither side proved able to deliver a decisive blow for the next two years, though protracted German action at Verdun throughout 1916,^[41] combined with the bloodletting at the Somme, brought the exhausted French army to the brink of collapse. Futile attempts at frontal assault came at a high price for both the British and the French poilu (infantry) and led to widespread mutinies, especially during the Nivelle Offensive.^[42]

Canadian troops advancing behind a British Mark II tank at the Battle of Vimy Ridge.

A French assault on German positions. Champagne, France, 1917.

Officers and senior enlisted men of the Bermuda Militia Artillery's Bermuda Contingent, Royal Garrison Artillery, in Europe.

A battleship squadron of the Hochseeflotte at sea

Throughout 1915–17, the British Empire and France suffered more casualties than Germany, because of both the strategic and tactical stances chosen by the sides. Strategically, while the Germans only mounted a single main offensive at Verdun, the Allies made several attempts to break through German lines. Tactically, German commander Erich Ludendorff's doctrine of "elastic defence" was well suited for trench warfare. This defence had a lightly defended forward position and a more powerful main position farther back beyond artillery range, from which an immediate and powerful counter-offensive could be launched.^[43][44]

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.^[45]

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.^[46]

Around 1.1 to 1.2 million soldiers from the British and Dominion armies were on the Western Front at any one time.^[47] A thousand battalions, occupying sectors of the line from the North Sea to the Orne River, 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 Poperinge or Amiens areas.

In the 1917 Battle of Arras, the only significant British military success was the capture of Vimy Ridge by the Canadian Corps under Sir Arthur Currie and Julian Byng. The assaulting troops could, for the first time, overrun, rapidly reinforce and hold the ridge defending the coal-rich Douai plain.^[48][49]

Naval war[link]

At the start of the war, the German Empire had cruisers scattered across the globe, some of which were subsequently used to attack Allied merchant shipping. The British Royal Navy systematically hunted them down, though not without some embarrassment from its inability to protect Allied shipping. For example, the German detached light cruiser SMS 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, most of the German East-Asia squadron—consisting of the armoured cruisers Scharnhorst and Gneisenau, light cruisers Nürnberg and Leipzig and two transport ships—did not have orders to raid shipping and was instead underway to Germany when it met British warships. The German flotilla and Dresden sank two armoured cruisers at the Battle of Coronel, but was almost destroyed at the Battle of the Falkland Islands in December 1914, with only Dresden and a few auxiliaries escaping, but at the Battle of Más a Tierra these too were destroyed or interned.^[50]

Soon after the outbreak of hostilities, Britain began a naval blockade of Germany. The strategy proved effective, cutting off vital military and civilian supplies, although this blockade violated accepted international law codified by several international agreements of the past two centuries.^[51] Britain mined international waters to prevent any ships from entering entire sections of ocean, causing danger to even neutral ships.^[52] Since there was limited response to this tactic, Germany expected a similar response to its unrestricted submarine warfare.^[53]

The 1916 Battle of Jutland (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, and one of the largest in history. It took place on 31 May – 1 June 1916, in the North Sea off Jutland. The Kaiserliche Marine's High Seas Fleet, commanded by Vice Admiral Reinhard Scheer, squared off against the Royal Navy's Grand Fleet, led by Admiral Sir John Jellicoe. The engagement was a stand off, as the Germans, outmanoeuvred 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.^[54]

German U-boats attempted to cut the supply lines between North America and Britain.^[55] The nature of submarine warfare meant that attacks often came without warning, giving the crews of the merchant ships little hope of survival.^[55][56] The United States launched a protest, and Germany changed its rules of engagement. After the notorious sinking of the passenger ship RMS Lusitania 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).^[57] Finally, in early 1917 Germany adopted a policy of unrestricted submarine warfare, realising the Americans would eventually enter the war.^[55][58] Germany sought to strangle Allied sea lanes before the U.S. could transport a large army overseas, but could maintain only five long-range U-boats on station, to limited effect.^[55]

U-155 exhibited near Tower Bridge in London after the First World War.

The U-boat threat lessened in 1917, when merchant ships began travelling in convoys, escorted by destroyers. This tactic made it difficult for U-boats to find targets, which significantly lessened losses; after the hydrophone and depth charges were introduced, accompanying destroyers might attack a submerged submarine with some hope of success. Convoys slowed the flow of supplies, since ships had to wait as convoys were assembled. The solution to the delays was an extensive program to build new freighters. Troopships were too fast for the submarines and did not travel the North Atlantic in convoys.^[59] The U-boats had sunk more than 5,000 Allied ships, at a cost of 199 submarines.^[60]

World War I also saw the first use of aircraft carriers in combat, with HMS Furious launching Sopwith Camels in a successful raid against the Zeppelin hangars at Tondern in July 1918, as well as blimps for antisubmarine patrol.^[61]

Southern theatres[link]

War in the Balkans[link]

Austrian troops executing captured Serbians. Serbia lost about 850,000 people, a quarter of its pre-war population.^[62]

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, Belgrade. A Serbian counter attack in the battle of Kolubara, 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 persuading Bulgaria to join in attacking Serbia. The Austro-Hungarian provinces of Slovenia, Croatia and Bosnia provided troops for Austria-Hungary, invading Serbia as well as fighting Russia and Italy. Montenegro allied itself with Serbia.^[63]

Serbia was conquered in a little more than a month, as the Central Powers, now including Bulgaria, sent in 600,000 troops. The Serbian army, fighting on two fronts and facing certain defeat, retreated into northern Albania (which they had invaded at the beginning of the war). The Serbs suffered defeat in the Battle of Kosovo. Montenegro covered the Serbian retreat towards the Adriatic coast in the Battle of Mojkovac in 6–7 January 1916, but ultimately the Austrians conquered Montenegro, too. The surviving 70,000 Serbian soldiers were evacuated by ship to Greece.^[64]

In late 1915, a Franco-British force landed at Salonica in Greece, to offer assistance and to pressure the government to declare war against the Central Powers. Unfortunately for the Allies, the pro-German King Constantine I dismissed the pro-Allied government of Eleftherios Venizelos, before the Allied expeditionary force could arrive.^[65] The friction between the king of Greece and the Allies continued to accumulate with the National Schism, which effectively divided Greece between regions still loyal to the king and the new provisional government of Venizelos in Salonica. After intensive diplomatic negotiations and an armed confrontation in Athens between Allied and royalist forces (an incident known as Noemvriana) the king of Greece resigned, and his second son Alexander took his place. Venizelos returned to Athens on 29 May 1917 and Greece, now unified, officially joined the war on the side of the Allies. The entire Greek army was mobilized and began to participate in military operations against the Central Powers on the Macedonian front.

Bulgarian soldiers in a trench, preparing to fire against an incoming airplane

After conquest, Serbia was divided between Austro-Hungary and Bulgaria. In 1917 the Serbs launched the Toplica Uprising and liberated for a short time the area between the Kopaonik mountains and the South Morava river. The uprising was crushed by joint efforts of Bulgarian and Austrian forces at the end of March 1917.

The Macedonian Front in the beginning was mostly static. French and Serbian forces retook limited areas of Macedonia by recapturing Bitola on 19 November 1916 as a result of the costly Monastir Offensive which brought stabilization of the front.

Serbian and French troops finally made a breakthrough, after most of the German and Austro-Hungarian troops had withdrawn. This breakthrough was significant in defeating Bulgaria and Austro-Hungary, which led to the final victory of WWI. The Bulgarians suffered their only defeat of the war at the Battle of Dobro Pole but days later, they decisively defeated British and Greek forces at the Battle of Doiran, avoiding occupation. After Serbian breakthrough of Bulgarian lines, Bulgaria capitulated on 29 September 1918.^[66] Hindenburg and Ludendorff concluded that the strategic and operational balance had now shifted decidedly against the Central Powers and a day after the Bulgarian collapse, during a meeting with government officials, insisted on an immediate peace settlement.^[67]

The disappearance of the Macedonian front meant that the road to Budapest and Vienna was now opened for the 670,000-strong army of general Franchet d'Esperey as the Bulgarian surrender deprived the Central Powers of the 278 infantry battalions and 1,500 guns (the equivalent of some 25 to 30 German divisions) that were previously holding the line.^[68] The German high command responded by sending only seven infantry and one cavalry division but these forces were far from enough for a front to be reestablished.^[68]

Ottoman Empire[link]

The Ottoman Empire joined the Central Powers in the war, the secret Ottoman-German Alliance having been signed in August 1914.^[69] It threatened Russia's Caucasian territories and Britain's communications with India via the Suez Canal. The British and French opened overseas fronts with the Gallipoli (1915) and Mesopotamian campaigns. In Gallipoli, the Ottoman Empire successfully repelled the British, French, and Australian and New Zealand Army Corps (ANZACs). In Mesopotamia, by contrast, after the disastrous Siege of Kut (1915–16), British Imperial forces reorganised and captured Baghdad in March 1917.

A British artillery battery emplaced on Mount Scopus in the Battle of Jerusalem.

Further to the west, the Suez Canal was successfully defended from Ottoman attacks in 1915 and 1916; in August a joint German and Ottoman force was defeated at the Battle of Romani by the Anzac Mounted and the 52nd (Lowland) Infantry Divisions. Following this victory, a British Empire Egyptian Expeditionary Force advanced across the Sinai Peninsula, pushing Ottoman forces back in the Battle of Magdhaba in December and the Battle of Rafa on the border between the Egyptian Sinai and Ottoman Palestine in January 1917. In March and April at the First and Second Battles of Gaza, German and Ottoman forces stopped the advance, but at the end of October the Sinai and Palestine Campaign resumed, when Allenby's XXth Corps, XXI Corps and Desert Mounted Corps won the Battle of Beersheba. Two Ottoman armies were defeated a few weeks later at the Battle of Mughar Ridge, and early in December Jerusalem was captured following another Ottoman defeat at the Battle of Jerusalem (1917). About this time Friedrich Freiherr Kress von Kressenstein was relieved of his duties as the Eighth Army's commander, replaced by Djevad Pasha, and a few months later the commander of the Ottoman Army in Palestine, Erich von Falkenhayn, was replaced by Otto Liman von Sanders.

A reorganised Egyptian Expeditionary Force, with an additional mounted division under Field Marshal Edmund Allenby, broke Ottoman forces at the Battle of Megiddo in September 1918. In six weeks, during virtually continuous operations, battles were successfully fought by British infantry and Australian, British, Indian and New Zealand, Light Horse, mounted Yeomanry, Lancers and Mounted Rifle brigades. They campaigned across the Jordan River to Amman in the east and northwards to capture Nablus and Tulkarm in the Judean Hills, and followed the Mediterranean coast into the Jezreel Valley (Esdraelon Plain), where Afula, Jenin and Nazareth were captured, along with Daraa east of the Jordan River on the Hejaz railway. Semakh and Tiberias on the Sea of Gallilee, were captured on the way northwards to Damascus and Aleppo. The Armistice of Mudros was signed on 30 October, when two and a half Ottoman armies had been defeated and captured.

Russian forest trench at the Battle of Sarikamish

Russian armies generally had the best of it in the Caucasus. Enver Pasha, supreme commander of the Ottoman armed forces, was ambitious and dreamed of re-conquering central Asia and areas that had been lost to Russia previously. He was, however, a poor commander.^[70] 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 Battle of Sarikamish.^[71]

General Yudenich, the Russian commander from 1915 to 1916, drove the Turks out of most of the southern Caucasus with a string of victories.^[71] In 1917, Russian Grand Duke Nicholas assumed command of the Caucasus front. Nicholas planned a railway from Russian Georgia 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 February Revolution and the Russian Caucasus Army began to fall apart.

German soldiers in Jerusalem

Instigated by the Arab bureau of the British Foreign Office, the Arab Revolt started with the help of Britain in June 1916 at the Battle of Mecca, led by Sherif Hussein of Mecca, and ended with the Ottoman surrender of Damascus. Fakhri Pasha, the Ottoman commander of Medina, resisted for more than two and half years during the Siege of Medina.^[72]

Along the border of Italian Libya and British Egypt, the Senussi tribe, incited and armed by the Turks, waged a small-scale guerrilla war against Allied troops. The British were forced to dispatch 12,000 troops to oppose them in the Senussi Campaign. Their rebellion was finally crushed in mid-1916.^[73]

Italian participation[link]

Austro-Hungarian mountain corps in Tyrol

Italy had been allied with the German and Austro-Hungarian Empires since 1882 as part of the Triple Alliance. However, the nation had its own designs on Austrian territory in Trentino, Istria, and Dalmatia. Rome had a secret 1902 pact with France, effectively nullifying its alliance.^[74] At the start of hostilities, Italy refused to commit troops, arguing that the Triple Alliance was defensive and that Austria–Hungary was an aggressor. The Austro-Hungarian government began negotiations to secure Italian neutrality, offering the French colony of Tunisia in return. The Allies made a counter-offer in which Italy would receive the Southern Tyrol, Julian March and territory on the Dalmatian coast after the defeat of Austria-Hungary. This was formalised by the Treaty of London. Further encouraged by the Allied invasion of Turkey in April 1915, Italy joined the Triple Entente and declared war on Austria-Hungary on 23 May. Fifteen months later Italy declared war on Germany.

a Hungarian soldier on the Italian front

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. Field Marshal Luigi Cadorna, a staunch proponent of the frontal assault, had dreams of breaking into the Slovenian plateau, taking Ljubljana and threatening Vienna. Cadorna's plan did not take into account the difficulties of the rugged Alpine terrain, or the technological changes that created trench warfare, giving rise to a series of bloody and inconclusive stalemated offensives.

Depiction of the Battle of Doberdò, fought in August 1916 between the Italian and Austro-Hungarian army.

On the Trentino front, the Austro-Hungarians took advantage of the mountainous terrain, which favoured the defender. After an initial strategic retreat, the front remained largely unchanged, while Austrian Kaiserschützen and Standschützen engaged Italian Alpini in bitter hand-to-hand combat throughout the summer. The Austro-Hungarians counterattacked in the Altopiano of Asiago, 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 Isonzo front along the Isonzo River, northeast of Trieste. 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 Gorizia. 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 Austro-Hungarian troops received large numbers of reinforcements, including German Stormtroopers and the elite Alpenkorps. The Central Powers launched a crushing offensive on 26 October 1917, spearheaded by the Germans. They achieved a victory at Caporetto. The Italian Army was routed and retreated more than 100 kilometres (62 mi) to reorganise, stabilising the front at the Piave River. Since in the Battle of Caporetto the 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 Piave River, and were finally decisively defeated in the Battle of Vittorio Veneto in October of that year. From 5–6 November 1918, Italian forces were reported to have reached Lissa, Lagosta, Sebenico, and other localities on the Dalmatian coast.^[75] By the end of hostilities in November 1918, the Italian military had seized control of the entire portion of Dalmatia that had been guaranteed to Italy by the London Pact.^[76] In 1918, Admiral Enrico Millo declared himself Italy's Governor of Dalmatia.^[76] Austria-Hungary surrendered in early November 1918.^[77][78]

Romanian participation[link]

Marshal Joffre inspecting Romanian troops

Romania had been allied with the Central Powers since 1882. When the war began, however, it declared its neutrality, arguing that because Austria-Hungary had itself declared war on Serbia, Romania was under no obligation to join the war. When the Entente Powers promised Romania large territories of eastern Hungary (Transylvania and Banat) that had a large Romanian population in exchange for Romania's declaring war on the Central Powers, the Romanian government renounced its neutrality, and on 27 August 1916 the Romanian Army launched an attack against Austria-Hungary, with limited Russian support. The Romanian offensive was initially successful, pushing back the Austro-Hungarian troops in Transylvania, but a counterattack by the forces of the Central Powers drove back the Russo-Romanian forces. As a result of the Battle of Bucharest the Central Powers occupied Bucharest on 6 December 1916. Fighting in Moldova continued in 1917, resulting in a costly stalemate for the Central Powers.^[79][80] Russian withdrawal from the war in late 1917 as a result of the October Revolution meant that Romania was forced to sign an armistice with the Central Powers on 9 December 1917.

In January 1918, Romanian forces established control over Bessarabia as the Russian Army abandoned the province. Although a treaty was signed by the Romanian and the Bolshevik Russian government following talks from 5–9 March 1918 on the withdrawal of Romanian forces from Bessarabia within two months, on 27 March 1918 Romania attached Bessarabia to its territory, formally based on a resolution passed by the local assembly of the territory on the unification with Romania.

Romania officially made peace with the Central Powers by signing the Treaty of Bucharest on 7 May 1918. Under that treaty, Romania was obliged to end war with the Central Powers and make small territorial concessions to Austria-Hungary, ceding control of some passes in the Carpathian Mountains, and grant oil concessions to Germany. In exchange, the Central Powers recognised the sovereignty of Romania over Bessarabia. The treaty was renounced in October 1918 by the Alexandru Marghiloman government, and Romania nominally re-entered the war on 10 November 1918. The next day, the Treaty of Bucharest was nullified by the terms of the Armistice of Compiègne.^[81][82] Total Romanian deaths from 1914 to 1918, military and civilian, within contemporary borders, were estimated at 748,000.^[83]

The role of India[link]

Contrary to British fears of a revolt in India, the outbreak of the war saw an unprecedented outpouring of loyalty and good will towards the United Kingdom.^[84][85] Indian political leaders from the Indian National Congress and other groups were eager to support the British war effort since they believed that strong support for the war effort would further the cause of Indian Home Rule. The Indian Army in fact outnumbered the British Army at the beginning of the war; about 1.3 million Indian soldiers and labourers served in Europe, Africa, and the Middle East, while both the central government and the princely states 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. Casualties of Indian soldiers totalled 47,746 killed and 65,126 wounded during World War I.^[86] The suffering engendered by the war as well as the failure of the British government to grant self-government to India after the end of hostilities bred disillusionment and fuelled the campaign for full independence that would be led by Mohandas Karamchand Gandhi and others.

Russian troops awaiting a German attack

Eastern Front[link]

Initial actions[link]