Opening hostilities

Confusion among the Central Powers

Germany 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 those had never been tested in exercises. Austro-Hungarian leaders believed Germany would cover its northern flank against Russia.^[60]

Serbian campaign

Thumb — Serbian Army Blériot XI "Oluj", 1915

Beginning on 12 August, the Austrians and Serbs clashed at the battles of the Cer and Kolubara; over the next two weeks, Austrian attacks were repulsed with heavy losses. As a result, Austria had to keep sizeable forces on the Serbian front, weakening their efforts against Russia.^[61] Serbia's victory against Austria-Hungary in the 1914 invasion has been called one of the major upset victories of the twentieth century.^[62] In 1915, the campaign saw the first use of anti-aircraft warfare after an Austrian plane was shot down with ground-to-air fire, as well as the first medical evacuation by the Serbian army.^[63]^[64]

German offensive in Belgium and France

Upon mobilisation, in accordance with the Schlieffen Plan, 80% of the German Army was located on the Western Front, with the remainder acting as a screening force in the East. Rather than a direct attack across their shared frontier, the German right wing would sweep through the Netherlands and Belgium, then swing south, encircling Paris and trapping the French army against the Swiss border. The plan's creator, Alfred von Schlieffen, head of the German General Staff from 1891 to 1906, estimated that this would take six weeks, after which the German army would transfer to the East and defeat the Russians.^[65]

The plan was substantially modified by his successor, Helmuth von Moltke the Younger. Under Schlieffen, 85% of German forces in the west were assigned to the right wing, with the remainder holding along the frontier. By keeping his left-wing deliberately weak, he hoped to lure the French into an offensive into the "lost provinces" of Alsace-Lorraine, which was the strategy envisaged by their Plan XVII.^[65] However, Moltke grew concerned that the French might push too hard on his left flank and as the German Army increased in size from 1908 to 1914, he changed the allocation of forces between the two wings to 70:30.^[66] He also considered Dutch neutrality essential for German trade and cancelled the incursion into the Netherlands, which meant any delays in Belgium threatened the viability of the plan.^[67] Historian Richard Holmes argues that these changes meant the right wing was not strong enough to achieve decisive success.^[68]

The initial German advance in the West was very successful. By the end of August, the Allied left, which included the British Expeditionary Force (BEF), was in full retreat, and the French offensive in Alsace-Lorraine was a disastrous failure, with casualties exceeding 260,000.^[69] German planning provided broad strategic instructions while allowing army commanders considerable freedom in carrying them out at the front, but von Kluck used this freedom to disobey orders, opening a gap between the German armies as they closed on Paris.^[70] The French army, reinforced by the British expeditionary corps, seized this opportunity to counter-attack and pushed the German army 40 to 80 km back. Both armies were then so exhausted that no decisive move could be implemented, so they settled in trenches, with the vain hope of breaking through as soon as they could build local superiority.

In 1911, the Russian Stavka agreed with the French to attack Germany within fifteen days of mobilisation, ten days before the Germans had anticipated, although it meant the two Russian armies that entered East Prussia on 17 August did so without many of their support elements.^[71]

By the end of 1914, German troops held strong defensive positions inside France, controlled the bulk of France's domestic coalfields, and inflicted 230,000 more casualties than it lost itself. However, communications problems and questionable command decisions cost Germany the chance of a decisive outcome, while it had failed to achieve the primary objective of avoiding a long, two-front war.^[72] As was apparent to several German leaders, this amounted to a strategic defeat; shortly after the First Battle of the Marne, Crown Prince Wilhelm told an American reporter "We have lost the war. It will go on for a long time but lost it is already."^[73]

Asia and the Pacific

On 30 August 1914, New Zealand occupied German Samoa (now Samoa). On 11 September, the Australian Naval and Military Expeditionary Force landed on the island of New Britain, then part of German New Guinea. On 28 October, the German cruiser SMS Emden sank the Russian cruiser Zhemchug in the Battle of Penang. Japan declared war on Germany before seizing territories in the Pacific, which later became the South Seas Mandate, as well as German Treaty ports on the Chinese Shandong peninsula at Tsingtao. After Vienna refused to withdraw its cruiser SMS Kaiserin Elisabeth from Tsingtao, Japan declared war on Austria-Hungary, and the ship was sunk in November 1914.^[74] Within a few months, Allied forces had seized all German territories in the Pacific, leaving only isolated commerce raiders and a few holdouts in New Guinea.^[75]^[76]

African campaigns

Some of the first clashes of the war involved British, French, and German colonial forces in Africa. On 6–7 August, French and British troops invaded the German protectorates of Togoland and Kamerun. 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 von Lettow-Vorbeck, fought a guerrilla warfare campaign and only surrendered two weeks after the armistice took effect in Europe.^[77]

Indian support for the Allies

Before the war, Germany had attempted to use Indian nationalism and pan-Islamism to its advantage, a policy continued post-1914 by instigating uprisings in India, while the Niedermayer–Hentig Expedition urged Afghanistan to join the war on the side of Central Powers. However, contrary to British fears of a revolt in India, the outbreak of the war saw a reduction in nationalist activity.^[78]^[79] Leaders from the Indian National Congress and other groups believed support for the British war effort would hasten Indian Home Rule, a promise allegedly made explicit in 1917 by Edwin Montagu, the Secretary of State for India.^[80]

In 1914, the British Indian Army was larger than the British Army itself, and between 1914 and 1918 an estimated 1.3 million Indian soldiers and labourers served in Europe, Africa, and the Middle East. In all, 140,000 soldiers served on the Western Front and nearly 700,000 in the Middle East, with 47,746 killed and 65,126 wounded.^[81] The suffering engendered by the war, as well as the failure of the British government to grant self-government to India afterward, bred disillusionment, resulting in the campaign for full independence led by Mahatma Gandhi.^[82]

Western Front 1914 to 1916

Trench warfare begins

Pre-war military tactics that had emphasised open warfare and individual riflemen proved obsolete when confronted with conditions prevailing in 1914. Technological advances allowed the creation of strong defensive systems largely impervious to massed infantry advances, such as barbed wire, machine guns and above all far more powerful artillery, which dominated the battlefield and made crossing open ground extremely difficult.^[83] Both sides struggled to develop tactics for breaching entrenched positions without heavy casualties. In time, technology enabled the production of new offensive weapons, such as gas warfare and the tank.^[84]

After the First Battle of the Marne in September 1914, Allied and German forces unsuccessfully tried to outflank each other, a series of manoeuvres later known as the "Race to the Sea". By the end of 1914, the opposing forces confronted each other along an uninterrupted line of entrenched positions from the Channel to the Swiss border.^[85] Since the Germans were normally able to choose where to stand, they generally held the high ground, while their trenches tended to be better built; those constructed by the French and English were initially considered "temporary", only needed until an offensive would destroy the German defences.^[86] 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. Several types of gas soon became widely used by both sides and though it never proved a decisive, battle-winning weapon, it became one of the most feared and best-remembered horrors of the war.^[87]^[88]

Continuation of trench warfare

In February 1916, the Germans attacked French defensive positions at the Battle of Verdun, lasting until December 1916. Casualties were greater for the French, but the Germans bled heavily as well, with anywhere from 700,000^[89] to 975,000^[90] casualties between the two combatants. Verdun became a symbol of French determination and self-sacrifice.^[91]

The Battle of the Somme was an Anglo-French offensive from July to November 1916. The opening day on 1 July 1916 was the bloodiest single day in the history of the British Army, which suffered 57,500 casualties, including 19,200 dead. As a whole, the Somme offensive led to an estimated 420,000 British casualties, along with 200,000 French and 500,000 Germans.^[92] The diseases that emerged in the trenches were a major killer on both sides. The living conditions led to disease and infection, such as trench foot, lice, typhus, trench fever, and the 'Spanish flu'.^[93]

Naval war

At the start of the war, German cruisers were scattered across the globe, some of which were subsequently used to attack Allied merchant shipping. These were systematically hunted down by the Royal Navy, though not before causing considerable damage. One of the most successful was the SMS Emden, part of the German East Asia Squadron stationed at Qingdao, which seized or sank 15 merchantmen, a Russian cruiser and a French destroyer. Most of the squadron was returning to Germany when it sank two British armoured cruisers at the Battle of Coronel in November 1914, before being virtually destroyed at the Battle of the Falkland Islands in December. The SMS Dresden escaped with a few auxiliaries, but after the Battle of Más a Tierra, these too were either destroyed or interned.^[94]

Soon after the outbreak of hostilities, Britain began a naval blockade of Germany. This proved effective in cutting off vital supplies, though it violated accepted international law.^[95] Britain also mined international waters which closed off entire sections of the ocean, even to neutral ships.^[96] Since there was limited response to this tactic, Germany expected a similar response to its unrestricted submarine warfare.^[97]

The Battle of Jutland^{[lower-alpha 12]} in May/June 1916 was the only full-scale clash of battleships during the war, and one of the largest in history. The clash was indecisive, though the Germans inflicted more damage than they received; thereafter the bulk of the German High Seas Fleet was confined to port.^[98]

German U-boats attempted to cut the supply lines between North America and Britain.^[99] The nature of submarine warfare meant that attacks often came without warning, giving the crews of the merchant ships little hope of survival.^[99]^[100] The United States launched a protest, and Germany changed its rules of engagement. After the 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 movement of crews to "a place of safety" (a standard that lifeboats did not meet).^[101] Finally, in early 1917, Germany adopted a policy of unrestricted submarine warfare, realising the Americans would eventually enter the war.^[99]^[102] Germany sought to strangle Allied sea lanes before the United States could transport a large army overseas, but, after initial successes, eventually failed to do so.^[99]

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, destroyers could potentially successfully attack a submerged submarine. Convoys slowed the flow of supplies since ships had to wait as convoys were assembled; the solution was an extensive program of building new freighters. Troopships were too fast for the submarines and did not travel the North Atlantic in convoys.^[103] The U-boats sunk more than 5,000 Allied ships, at the cost of 199 submarines.^[104]

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.^[105]

Southern theatres

War in the Balkans

Faced with Russia in the east, 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 succeeded in driving them from the country by the end of 1914. For the first 10 months of 1915, Austria-Hungary used most of its military reserves to fight Italy. German and Austro-Hungarian diplomats scored a coup by persuading Bulgaria to join the attack on Serbia.^[106] The Austro-Hungarian provinces of Slovenia, Croatia and Bosnia provided troops for Austria-Hungary. Montenegro allied itself with Serbia.^[107]

Bulgaria declared war on Serbia on 14 October 1915 and joined in the attack by the Austro-Hungarian army under Mackensen's army of 250,000 that was already underway. Serbia was conquered in a little more than a month, as the Central Powers, now including Bulgaria, sent in 600,000 troops in total. The Serbian army, fighting on two fronts and facing certain defeat, retreated into northern Albania. The Serbs suffered defeat in the Battle of Kosovo. Montenegro covered the Serbian retreat toward the Adriatic coast in the Battle of Mojkovac on 6–7 January 1916, but ultimately the Austrians also conquered Montenegro. The surviving Serbian soldiers were evacuated to Greece.^[108] After the conquest, Serbia was divided between Austro-Hungary and Bulgaria.^[109]

In late 1915, a Franco-British force landed at Salonica in Greece to offer assistance and to pressure its government to declare war against the Central Powers. However, the pro-German King Constantine I dismissed the pro-Allied government of Eleftherios Venizelos before the Allied expeditionary force arrived.^[110]

The Macedonian front was at first mostly static. French and Serbian forces retook limited areas of Macedonia by recapturing Bitola on 19 November 1916 following the costly Monastir offensive, which brought stabilisation of the front.^[111]

Serbian and French troops finally made a breakthrough in September 1918 in the Vardar offensive, after most German and Austro-Hungarian troops had been withdrawn. The Bulgarians were defeated at the Battle of Dobro Pole, and by 25 September British and French troops had crossed the border into Bulgaria proper as the Bulgarian army collapsed. Bulgaria capitulated four days later, on 29 September 1918.^[113] The German high command responded by despatching troops to hold the line, but these forces were too weak to re-establish a front.^[114]

The disappearance of the Macedonian front meant that the road to Budapest and Vienna was now opened to Allied forces. 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, insisted on an immediate peace settlement.^[115]

Ottoman Empire

The Ottomans threatened Russia's Caucasian territories and Britain's communications with India via the Suez Canal. The Ottoman Empire took advantage of the European powers' preoccupation with the war and conducted large-scale ethnic cleansing of the Armenian, Greek, and Assyrian Christian populations—the Armenian genocide, Greek genocide, and Sayfo respectively.^[116]^[117]^[118]

The British and French opened overseas fronts with the Gallipoli (1915) and Mesopotamian campaigns (1914). In Gallipoli, the Ottoman Empire successfully repelled the British, French, and Australian and New Zealand Army Corps (ANZACs). In Mesopotamia, by contrast, after the defeat of the British defenders in the siege of Kut by the Ottomans (1915–1916), British Imperial forces reorganised and captured Baghdad in March 1917. The British were aided in Mesopotamia by local Arab and Assyrian fighters, while the Ottomans employed local Kurdish and Turcoman tribes.^[119]

The Suez Canal was defended from Ottoman attacks in 1915 and 1916; in August 1916, a German and Ottoman force was defeated at the Battle of Romani by the ANZAC Mounted Division and the 52nd (Lowland) Infantry Division. Following this victory, an 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.^[120]

Thumb — Russian forest trench at the Battle of Sarikamish, 1914–1915

Russian armies generally had success in the Caucasus campaign. Enver Pasha, supreme commander of the Ottoman armed forces, dreamed of re-conquering central Asia and areas that had been previously lost to Russia. He was, however, a poor commander.^[121] 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.^[122] General Yudenich, the Russian commander from 1915 to 1916, drove the Turks out of most of the southern Caucasus.^[122]

The Ottoman Empire, with German support, invaded Persia (modern Iran) in December 1914 to cut off British and Russian access to petroleum reservoirs around Baku.^[123] Persia, ostensibly neutral, had long been under British and Russian influence. The Ottomans and Germans were aided by Kurdish and Azeri forces, together with a large number of major Iranian tribes, while the Russians and British had the support of Armenian and Assyrian forces. The Persian campaign lasted until 1918 and ended in failure for the Ottomans and their allies. However, the Russian withdrawal from the war in 1917 led Armenian and Assyrian forces to be cut off from supply lines, outnumbered, outgunned and isolated, forcing them to fight and flee towards British lines in northern Mesopotamia.^[124]

The Arab Revolt, instigated by the British Foreign Office, started in June 1916 with the Battle of Mecca, led by Sharif Hussein. The Sharif declared the independence of the Kingdom of Hejaz and, with British assistance, conquered much of Ottoman-held Arabia, resulting finally in the Ottoman surrender of Damascus. Fakhri Pasha, the Ottoman commander of Medina, resisted for more than 2+1⁄2 years during the siege of Medina before surrendering in January 1919.^[125]

The Senussi tribe, along the border of Italian Libya and British Egypt, 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.^[126]

Total Allied casualties on the Ottoman fronts amounted to 650,000 men. Total Ottoman casualties were 725,000, with 325,000 dead and 400,000 wounded.^[127]

Italian Front

Though Italy joined the Triple Alliance in 1882, a treaty with its traditional Austrian enemy was so controversial that subsequent governments denied its existence and the terms were only made public in 1915.^[128] This arose from nationalist designs on Austro-Hungarian territory in Trentino, the Austrian Littoral, Rijeka and Dalmatia, considered vital to secure the borders established in 1866.^[129] In 1902, Rome secretly had agreed with France to remain neutral if the latter was attacked by Germany, effectively nullifying its role in the Triple Alliance.^[130]

When the war began in 1914, Italy argued the Triple Alliance was defensive and it was not obliged to support an Austrian attack on Serbia. Opposition to joining the Central Powers increased when Turkey became a member in September, since in 1911 Italy had occupied Ottoman possessions in Libya and the Dodecanese islands.^[131] To secure Italian neutrality, the Central Powers offered them Tunisia, while in return for an immediate entry into the war, the Allies agreed to their demands for Austrian territory and sovereignty over the Dodecanese.^[132] Although they remained secret, these provisions were incorporated into the April 1915 Treaty of London; Italy joined the Triple Entente and, on 23 May, declared war on Austria-Hungary,^[133] followed by Germany fifteen months later.

The pre-1914 Italian army was short of officers, trained men, adequate transport and modern weapons; by April 1915, some of these deficiencies had been remedied but it was still unprepared for the major offensive required by the Treaty of London.^[134] The advantage of superior numbers was offset by the difficult terrain; much of the fighting took place high in the Alps and Dolomites, where trench lines had to be cut through rock and ice and keeping troops supplied was a major challenge. These issues were exacerbated by unimaginative strategies and tactics.^[135] Between 1915 and 1917, the Italian commander, Luigi Cadorna, undertook a series of frontal assaults along the Isonzo, which made little progress and cost many lives; by the end of the war, Italian combat deaths totalled around 548,000.^[136]

In the spring of 1916, the Austro-Hungarians counterattacked in Asiago in the Strafexpedition, but made little progress and were pushed by the Italians back to Tyrol.^[137] Although Italy occupied southern Albania in May 1916, their main focus was the Isonzo front which, after the capture of Gorizia in August 1916, remained static until October 1917. After a combined Austro-German force won a major victory at Caporetto, Cadorna was replaced by Armando Diaz who retreated more than 100 kilometres (62 mi) before holding positions along the Piave River.^[138] A second Austrian offensive was repulsed in June 1918. On 24 October, Diaz launched the Battle of Vittorio Veneto and initially met stubborn resistance,^[139] but with Austria-Hungary collapsing, Hungarian divisions in Italy demanded they be sent home.^[140] When this was granted, many others followed and the Imperial army disintegrated, the Italians taking over 300,000 prisoners.^[141] On 3 November, the Armistice of Villa Giusti ended hostilities between Austria-Hungary and Italy which occupied Trieste and areas along the Adriatic Sea awarded to it in 1915.^[142]

Eastern Front

Initial actions

As previously agreed with French president Raymond Poincaré, Russian plans at the start of the war were to simultaneously advance into Austrian Galicia and East Prussia as soon as possible. Although their attack on Galicia was largely successful, and the invasions achieved their aim of forcing Germany to divert troops from the Western Front, the speed of mobilisation meant they did so without much of their heavy equipment and support functions. These weaknesses contributed to Russian defeats at Tannenberg and the Masurian Lakes in August and September 1914, forcing them to withdraw from East Prussia with heavy losses.^[143]^[144] By spring 1915, they had also retreated from Galicia, and the May 1915 Gorlice–Tarnów offensive allowed the Central Powers to invade Russian-occupied Poland.^[145]

Despite the successful June 1916 Brusilov offensive against the Austrians in eastern Galicia,^[146] shortages of supplies, heavy losses and command failures prevented the Russians from fully exploiting their victory. However, it was one of the most significant offensives of the war, diverting German resources from Verdun, relieving Austro-Hungarian pressure on the Italians, and convincing Romania to enter the war on the side of the Allies on 27 August. It also fatally weakened both the Austrian and Russian armies, whose offensive capabilities were badly affected by their losses and increased disillusion with the war that ultimately led to the Russian revolutions.^[147]

Meanwhile, unrest grew in Russia as the Tsar remained at the front, with the home front controlled by Empress Alexandra. Her increasingly incompetent rule and food shortages in urban areas led to widespread protests and the murder of her favourite, Grigori Rasputin, at the end of 1916.^[148]

Romanian participation

Bucharest

Timișoara (Banat)

Cluj (Transylvania)

Chișinău (Moldova)

Constanța (Dobruja)

Bulgaria

Hungary

Mărășești

Oituz

Romania key locations 1916–1918 (note; using 2022 borders)

Despite secretly agreeing to support the Triple Alliance in 1883, Romania increasingly found itself at odds with the Central Powers over their support for Bulgaria in the Balkan Wars and the status of ethnic Romanian communities in Hungarian-controlled Transylvania,^[149] which comprised an estimated 2.8 million of the 5.0 million population.^[150] With the ruling elite split into pro-German and pro-Entente factions,^[151] Romania remained neutral for two years while allowing Germany and Austria to transport military supplies and advisors across Romanian territory.^[152]

In September 1914, Russia acknowledged Romanian rights to Austro-Hungarian territories including Transylvania and Banat, whose acquisition had widespread popular support,^[150] and Russian success against Austria led Romania to join the Entente in the August 1916 Treaty of Bucharest.^[152] Under the strategic plan known as Hypothesis Z, the Romanian army planned an offensive into Transylvania, while defending Southern Dobruja and Giurgiu against a possible Bulgarian counterattack.^[153] On 27 August 1916, they attacked Transylvania and occupied substantial parts of the province before being driven back by the recently formed German 9th Army, led by former Chief of Staff Erich von Falkenhayn.^[154] A combined German-Bulgarian-Turkish offensive captured Dobruja and Giurgiu, although the bulk of the Romanian army managed to escape encirclement and retreated to Bucharest, which surrendered to the Central Powers on 6 December 1916.^[155]

In the summer of 1917, a Central Powers offensive began in Romania under the command of August von Mackensen to knock Romania out of the war, resulting in the battles of Oituz, Mărăști and Mărășești where up to 1,000,000 Central Powers troops were present. The battles lasted from 22 July to 3 September and eventually, the Romanian army was victorious advancing 500 km². August von Mackensen could not plan for another offensive as he had to transfer troops to the Italian Front.^[156] Following the Russian revolution, Romania found itself alone on the Eastern Front and signed the Treaty of Bucharest with the Central Powers, which recognised Romanian sovereignty over Bessarabia in return for ceding control of passes in the Carpathian Mountains to Austria-Hungary and leasing its oil wells to Germany. Although approved by Parliament, King Ferdinand I refused to sign it, hoping for an Allied victory in the west.^[157] Romania re-entered the war on 10 November 1918 on the side of the Allies and the Treaty of Bucharest was formally annulled by the Armistice of 11 November 1918.^[158]^{[lower-alpha 13]}

Central Powers peace overtures

On 12 December 1916, after ten brutal months of the Battle of Verdun and a successful offensive against Romania, Germany attempted to negotiate a peace with the Allies.^[160] However, this attempt was rejected out of hand as a "duplicitous war ruse".^[160]

US president Woodrow Wilson attempted to intervene as a peacemaker, asking for both sides to state their demands. Lloyd George's War Cabinet considered the German offer to be a ploy to create divisions among the Allies. After initial outrage and much deliberation, they took Wilson's note as a separate effort, signalling that the US was on the verge of entering the war against Germany following the "submarine outrages". While the Allies debated a response to Wilson's offer, the Germans chose to rebuff it in favour of "a direct exchange of views". Learning of the German response, the Allied governments were free to make clear demands in their response of 14 January. They sought restoration of damages, the evacuation of occupied territories, reparations for France, Russia and Romania, and a recognition of the principle of nationalities.^[161] The Allies sought guarantees that would prevent or limit future wars.^[162] The negotiations failed and the Entente powers rejected the German offer on the grounds of honour, and noted Germany had not put forward any specific proposals.^[160]

Final years of the war

Russian Revolution and withdrawal

By the end of 1916, Russian casualties totalled nearly five million killed, wounded or captured, with major urban areas affected by food shortages and high prices. In March 1917, Tsar Nicholas ordered the military to forcibly suppress strikes in Petrograd but the troops refused to fire on the crowds.^[163] Revolutionaries set up the Petrograd Soviet and fearing a left-wing takeover, the State Duma forced Nicholas to abdicate and established the Russian Provisional Government, which confirmed Russia's willingness to continue the war. However, the Petrograd Soviet refused to disband, creating competing power centres and causing confusion and chaos, with frontline soldiers becoming increasingly demoralised.^[164]

Following the Tsar's abdication, Vladimir Lenin—with the help of the German government—was ushered from Switzerland into Russia on 16 April 1917. Discontent and the weaknesses of the Provisional Government led to a rise in the popularity of the Bolshevik Party, led by Lenin, which demanded an immediate end to the war. The Revolution of November was followed in December by an armistice and negotiations with Germany. At first, the Bolsheviks refused the German terms, but when German troops began marching across Ukraine unopposed, they acceded to the Treaty of Brest-Litovsk on 3 March 1918. The treaty ceded vast territories, including Finland, Estonia, Latvia, Lithuania, and parts of Poland and Ukraine to the Central Powers.^[165]

With the Russian Empire out of the war, Romania found itself alone on the Eastern Front and signed the Treaty of Bucharest with the Central Powers in May 1918. Under the terms of the treaty, Romania ceded territory to Austria-Hungary and Bulgaria and leased its oil reserves to Germany. However, the terms also included the Central Powers' recognition of the union of Bessarabia with Romania.^[166]^[167]

United States enters the war

The United States was a major supplier of war material to the Allies but remained neutral in 1914, in large part due to domestic opposition.^[168] The most significant factor in creating the support Wilson needed was the German submarine offensive, which not only cost American lives but paralysed trade as ships were reluctant to put to sea.^[169]

On 6 April 1917, Congress declared war on Germany as an "Associated Power" of the Allies.^[170] The US Navy sent a battleship group to Scapa Flow to join the Grand Fleet, and provided convoy escorts. In April 1917, the US Army had fewer than 300,000 men, including National Guard units, compared to British and French armies of 4.1 and 8.3 million respectively. The Selective Service Act of 1917 drafted 2.8 million men, though training and equipping such numbers was a huge logistical challenge. By June 1918, over 667,000 members of the American Expeditionary Forces (AEF) were transported to France, a figure which reached 2 million by the end of November.^[171]

Despite his conviction that Germany must be defeated, Wilson went to war to ensure the US played a leading role in shaping the peace, which meant preserving the AEF as a separate military force, rather than being absorbed into British or French units as his Allies wanted.^[172] He was strongly supported by AEF commander General John J. Pershing, a proponent of pre-1914 "open warfare" who considered the French and British emphasis on artillery misguided and incompatible with American "offensive spirit".^[173] Much to the frustration of his Allies, who had suffered heavy losses in 1917, he insisted on retaining control of American troops, and refused to commit them to the front line until able to operate as independent units. As a result, the first significant US involvement was the Meuse–Argonne offensive in late September 1918.^[174]

Nivelle Offensive (April–May 1917)

In December 1916, Robert Nivelle replaced Pétain as commander of French armies on the Western Front and began planning a spring attack in Champagne, part of a joint Franco-British operation.^[175] Poor security meant German intelligence was well informed on tactics and timetables, but despite this, when the attack began on 16 April the French made substantial gains, before being brought to a halt by the newly built and extremely strong defences of the Hindenburg Line. Nivelle persisted with frontal assaults and, by 25 April, the French had suffered nearly 135,000 casualties, including 30,000 dead, most incurred in the first two days.^[176]

Concurrent British attacks at Arras were more successful, though ultimately of little strategic value.^[177] Operating as a separate unit for the first time, the Canadian Corps' capture of Vimy Ridge is viewed by many Canadians as a defining moment in creating a sense of national identity.^[178]^[179] Though Nivelle continued the offensive, on 3 May the 21st Division, which had been involved in some of the heaviest fighting at Verdun, refused orders to go into battle, initiating the French Army mutinies; within days, "collective indiscipline" had spread to 54 divisions, while over 20,000 deserted.^[180]

Sinai and Palestine campaign (1917–1918)

In March and April 1917, at the First and Second Battles of Gaza, German and Ottoman forces stopped the advance of the Egyptian Expeditionary Force, which had begun in August 1916 at the Battle of Romani.^[181]^[182] At the end of October 1917, the Sinai and Palestine campaign resumed, when General Edmund Allenby's XXth Corps, XXI Corps and Desert Mounted Corps won the Battle of Beersheba.^[183] Two Ottoman armies were defeated a few weeks later at the Battle of Mughar Ridge and, early in December, Jerusalem had been captured following another Ottoman defeat at the Battle of Jerusalem.^[184]^[185]^[186] 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.^[187]^[188]

In early 1918, the front line was extended and the Jordan Valley was occupied, following the First Transjordan and the Second Transjordan attacks by British Empire forces in March and April 1918.^[189]

German offensive and Allied counter-offensive (March–November 1918)

Thumb — Between April and November 1918, the Allies increased their front-line rifle strength while German strength fell by half.^[190]

In December 1917, the Central Powers signed an armistice with Russia, thus freeing large numbers of German troops for use in the West. With German reinforcements and new American troops pouring in, the 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 success in a final quick offensive.^[191] Ludendorff drew up plans (Operation Michael) for the 1918 offensive on the Western Front. The operation commenced on 21 March 1918, with an attack on British forces near Saint-Quentin. German forces achieved an unprecedented advance of 60 kilometres (37 mi).^[192] The initial offensive was a success; after heavy fighting, however, the offensive was halted. Lacking tanks or motorised artillery, the Germans were unable to consolidate their gains. The problems of re-supply were also exacerbated by increasing distances that now stretched over terrain that was shell-torn and often impassable to traffic.^[193] Germany launched Operation Georgette against the northern English Channel ports. The Allies halted the drive after limited territorial gains by Germany. The German Army to the south then conducted Operations Blücher and Yorck, pushing broadly towards Paris. Germany launched Operation Marne (Second Battle of the Marne) on 15 July, in an attempt to encircle Reims. The resulting counter-attack, which started the Hundred Days Offensive on 8 August,^[194] led to a marked collapse in German morale.^[195]^[196]^[197]

Allied advance to the Hindenburg Line

Thumb — American soldiers firing on German entrenched positions during the Meuse-Argonne offensive, 1918

By September, the Germans had fallen back to the Hindenburg Line. The Allies had advanced to the Hindenburg Line in the north and centre. German forces launched numerous counterattacks, but positions and outposts of the Line continued falling, with the BEF alone taking 30,441 prisoners in the last week of September. On 24 September, the Supreme Army Command informed the leaders in Berlin that armistice talks were inevitable.^[198]

The final assault on the Hindenburg Line began with the Meuse-Argonne offensive, launched by American and French troops on 26 September. Two days later the Belgians, French and British attacked around Ypres, and the day after the British at St Quentin in the centre of the line. The following week, cooperating American and French units broke through in Champagne at the Battle of Blanc Mont Ridge (3–27 October), forcing the Germans off the commanding heights, and closing towards the Belgian frontier.^[199] On 8 October, the Hindenburg Line was pierced by British and Dominion troops of the First and Third British Armies at the Second Battle of Cambrai.^[200]

Breakthrough of Macedonian front (September 1918)

Allied forces started the Vardar offensive on 15 September at two key points: Dobro Pole and near Dojran Lake. In the Battle of Dobro Pole, the Serbian and French armies had success after a three-day-long battle with relatively small casualties, and subsequently made a breakthrough in the front, something which was rarely seen in World War I. After the front was broken, Allied forces started to liberate Serbia and reached Skopje at 29 September, after which Bulgaria signed an armistice with the Allies on 30 September.^[201]^[202]

Armistices and capitulations

The collapse of the Central Powers came swiftly. Bulgaria was the first to sign an armistice, the Armistice of Salonica on 29 September 1918.^[203] German Emperor Wilhelm II in a telegram to Bulgarian Tsar Ferdinand I described the situation thus: "Disgraceful! 62,000 Serbs decided the war!".^[204]^[205] On the same day, the German Supreme Army Command informed Kaiser Wilhelm II and the Imperial Chancellor Count Georg von Hertling, that the military situation facing Germany was hopeless.^[206]

On 24 October, the Italians began a push that rapidly recovered territory lost after the Battle of Caporetto. This culminated in the Battle of Vittorio Veneto, marking the end of the Austro-Hungarian Army as an effective fighting force. The offensive also triggered the disintegration of the 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 flag of truce and accepted the Armistice of Villa Giusti, arranged with the Allied Authorities in Paris. Austria and Hungary signed separate armistices following the overthrow of the Habsburg monarchy. In the following days, the Italian Army occupied Innsbruck and all Tyrol, with over 20,000 soldiers.^[207]

On 30 October, the Ottoman Empire capitulated, and signed the Armistice of Mudros.^[203]

German government surrenders

Thumb — Ferdinand Foch (*second from right*) pictured outside the carriage in Compiègne after agreeing to the armistice that ended the war there.^[208]

With the military faltering and with widespread loss of confidence in the Kaiser leading to his abdication and fleeing of the country, Germany moved towards surrender. Prince Maximilian of Baden took charge on October 3 as Chancellor of Germany. Negotiations with President Wilson began immediately, in the hope that he would offer better terms than the British and French. Wilson demanded a constitutional monarchy and parliamentary control over the German military.^[209]

The German Revolution of 1918–1919 began at the end of October 1918. Units of the German Navy refused to set sail for a last, large-scale operation in a war they believed to be as good as lost. The sailors' revolt, which then ensued in the naval ports of Wilhelmshaven and Kiel, spread across the whole country within days and led to the proclamation of a republic on 9 November 1918, shortly thereafter to the abdication of Kaiser Wilhelm II, and German surrender.^[210]^[211]^[212]^[213]^[214]