World War I

World War I lasted from 28 July 1914, when Austria-Hungary declared war on Serbia, to the Armistice that took effect at 11 a.m. on 11 November 1918.¹ The Central Powers — Germany, Austria-Hungary, the Ottoman Empire and Bulgaria — faced the Allies: France, Great Britain, Russia, Italy, Japan and, from 1917, the United States.² Over 30 nations declared war between 1914 and 1918, the majority on the side of the Allies.³ The US War Department's February 1924 table counted 65,038,810 men mobilised across all the belligerents.⁴

The war was one of the great watersheds of twentieth-century geopolitical history.¹ It brought down four great imperial dynasties — in Germany, Russia, Austria-Hungary and Turkey — produced the Bolshevik Revolution in Russia, and laid the groundwork for World War II.¹ The settlements that followed were imposed by the victors rather than negotiated, and have been criticised ever since as laying the foundations of future conflicts.⁵

The casualties dwarfed those of previous wars: some 8,500,000 soldiers died as a result of wounds and/or disease.⁴ Around 13,000,000 civilian deaths are attributed to the war — largely from starvation, exposure, disease, military encounters and massacres.⁴ The Imperial War Museums estimate 16 million soldiers and civilians dead in total.³ Such counts differ because the main sources are army statistics, and the definitions behind the headings vary between sources.⁶

By 1914 Europe was divided into two rival alliance systems.⁷ Germany formed an alliance with neighbouring Austria-Hungary in 1879, and Italy joined three years later.⁷ Fear of Germany's growing strength encouraged Russia and France to enter into an alliance in 1893.⁷ Britain settled its colonial disputes with France and Russia from 1904.⁷

On 28 June 1914 Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne, and his wife were assassinated by a Serbian-backed terrorist.⁷ With the guarantee of German backing, Austria-Hungary issued an ultimatum to Serbia on 23 July, intent on starting a war.⁷ Serbia conceded all of the ultimatum's terms except the involvement of Austro-Hungarian officials in an inquiry into the assassination, and Austria rejected that reply.⁷

With German encouragement, Austria-Hungary declared war on Serbia on 28 July, and Russia ordered its forces to prepare for war on 30 July — a mobilisation the Russians viewed as a precaution but Germany saw as an aggressive act.⁷ Germany declared war on Russia on 1 August and on France on 3 August.⁷ Germany's violation of Belgian neutrality brought Britain and its empire into the war on 4 August, after an ultimatum demanding withdrawal expired at 11pm without a reply.⁷

The German plan for a rapid victory in the west failed: the French and British counter-offensive at the Marne (6–10 September 1914) forced the Germans to retreat after several days of bitter fighting.⁸ The Marne marked the end of mobile warfare on the Western Front.⁸ Re-engaging Allied forces on the Aisne, the Germans saw the fighting stagnate into trench warfare.⁸ In the east, Tannenberg meant a long, multi-front war.⁸

Attempting to outflank each other, Allied and German troops could not win a decisive victory at the First Battle of Ypres in October–November 1914, and trench warfare set in.² Losses on all fronts for the year 1914 topped five million, with a million men killed.⁸ By the end of 1914, after just five months of fighting, the number of dead and wounded exceeded four million men.⁹

The war became global: Britain's empire, Japan, the Ottoman Empire and Bulgaria all entered the conflict.² Trenches and machine guns turned the Western Front into a siege that neither side could break.⁸ New weapons — gas, tanks and aircraft — would be deployed on an industrial scale before the war ended.¹⁰

The trench systems on the Western Front were roughly 475 miles long, stretching from the English Channel to the Swiss Alps, although not in a continuous line.⁹ Beginning as simple ditches, the trenches evolved into complex networks stretching over 250 miles (402 kilometres) through France and Belgium.¹⁰ Over 6 million British and British Empire soldiers were treated for sickness during the war, a figure that could have been far higher without improvements in sanitation and medical care.¹⁰

The modern machine gun, developed in the 1880s and 1890s, was a reliable belt-fed gun capable of sustained rates of extremely rapid fire: it could fire 600 bullets per minute with a range of more than 1,000 yards (900 metres).¹ The greatest number of casualties and wounds were inflicted by artillery, followed by small arms, and then by poison gas.⁴ The first significant gas attack occurred at Ypres in April 1915, when the Germans released clouds of poisonous chlorine.¹⁰

The internal combustion engine, armour plate and the continuous track, combined with the problem of trench warfare, facilitated the production of the tank.¹⁰ The soldiers' world was one of sandbags, duckboards and barbed wire, overlooked by machine guns.¹⁰ The result was attrition: an unbroken siege fought at enormous cost.⁸

Hoping to bleed France white, the German Army launched a major offensive against the symbolic fortress of Verdun on 21 February 1916.² The Battle of Verdun, 21 February to 18 December 1916, was the longest battle of the First World War, and also one of the costliest.⁸ The Germans lost over 430,000 men killed or wounded, and the French approximately 550,000.⁸

On 1 July 1916, the first day of the Battle of the Somme, British casualties numbered over 57,000, of which 19,240 were killed — the bloodiest day in British military history.⁸ Over the next 141 days the British advanced a maximum of seven miles.⁸ More than one million men from all sides were killed, wounded or captured.⁸

At sea, Jutland (31 May – 1 June 1916) was the largest naval battle of the war, involving 250 ships and around 100,000 men.⁸ The British lost 14 ships and over 6,000 men; the Germans lost 11 ships and over 2,500 men.⁸ Germany never again seriously challenged British control of the North Sea.⁸

The Brusilov Offensive (4 June – 20 September 1916) was the most successful Russian offensive — and one of the most successful breakthrough operations — of the First World War.⁸ It placed severe strain on Austria-Hungary.⁸

The Gallipoli campaign, 25 April 1915 to 9 January 1916, was the land-based element of a strategy intended to allow Allied ships to pass through the Dardanelles, capture Constantinople (now Istanbul) and knock Ottoman Turkey out of the war.⁸ At dawn on 25 April 1915 Allied troops landed on the Gallipoli peninsula in Ottoman Turkey.⁸ The campaign failed; its most successful operation was the evacuation of 19 and 20 December, covered by a carefully planned deception that kept Turkish casualties to very few.¹¹

Italy entered the war in May 1915.⁸ After the setbacks of 1917, including Caporetto, the Italian Army severely defeated Austro-Hungarian forces at Vittorio Veneto (24 October – 3 November 1918), ending the war on the Italian Front.² The defeat ushered in the final dissolution of the Austro-Hungarian Empire.²

Ottoman forces fought the Allies at Gallipoli, in Mesopotamia and along the Suez Canal.⁸ Great Britain and France secretly signed the Sykes-Picot Agreement on 16 May 1916, assuming they would defeat the Ottoman Empire, to divide the Middle East between them.² France claimed Syria and Lebanon; Britain claimed Jordan, Iraq, the Gulf states and the Palestine Mandate.²

Arab nationalists revolted against Ottoman rule in the Great Arab Rising of 5 June 1916.² It was encouraged by British pledges given during the Hussein-McMahon correspondence of 1915–16.¹² Hussein ibn Ali, the Hashemite sharif of Mecca, brought the Arabs of the Hejaz into revolt against the Turks, based on the understanding that the Arabs would eventually receive independence.¹² The secret Sykes-Picot arrangement conflicted with those pledges.¹²

Jerusalem was captured on 9 December 1917.⁸ The Battle of Megiddo (19–25 September 1918) marked the beginning of the final British-led offensive in the Sinai and Palestine Campaign.⁸ British and Commonwealth forces broke through the Ottoman lines with an advance of over 30km on the first day, and the Desert Mounted Corps pushed through gaps to encircle the Ottoman troops.⁸ Victory opened the way to Damascus, which Australian troops entered on 1 October.⁸ On 30 October the Ottoman Empire sought a peace settlement, and an armistice was signed at Mudros, with hostilities ceasing at 12 noon the following day.⁸

The United States remained neutral when the war began.¹³ On 4 February 1915 Germany initiated a policy of unrestricted submarine warfare, under which all merchant ships, including those of neutral countries, would be subject to attack.² On 7 May 1915 a German U-boat torpedoed the Lusitania, a British passenger liner, killing 128 Americans.² Germany pledged to suspend unrestricted submarine warfare, under the Sussex pledge of May 1916.¹³

On 19 January 1917 British naval intelligence intercepted and decrypted a telegram sent by German Foreign Minister Arthur Zimmermann to the German Ambassador in Mexico City.¹³ Unrestricted submarine warfare resumed on 1 February 1917.¹³ President Woodrow Wilson went before a joint session of Congress on 2 April 1917 to request a declaration of war against Germany.¹³ He cited Germany's violation of its pledge and its attempts to entice Mexico into an alliance against the United States.¹³ The United States later declared war on Austria-Hungary on 7 December 1917.¹³

By the end of August 1918 there were over 1.4 million American troops in France.¹⁴ During the 1918 offensives they were arriving at a rate of about 300,000 men per month.¹ That flow of fresh divisions gave the Allies the decisive weight in the final year of the war.¹

Operation Michael, the first of the German Spring Offensives, began on the damp and misty morning of 21 March 1918, preceded by an artillery bombardment using 6,000 guns.⁸ The Germans hoped for a decisive victory before the industrial strength of the United States could be fully mobilised.¹¹ They advanced 64 kilometres past the Somme battlefields of 1916 before losing momentum.¹¹ On 11 April Field Marshal Sir Douglas Haig issued a special order of the day, using the phrase Backs to the Wall to sum up the desperate fighting.⁸ The great offensives cost the Germans a total of 800,000 casualties.¹

At 4.20am on 8 August 1918 the Battle of Amiens began in a morning of heavy fog, taking the Germans completely by surprise.¹⁴ The Australian Corps and the Canadian Corps spearheaded the attack behind 534 tanks, reaching their objectives within hours.¹⁴ Ludendorff called 8 August the black day of the German Army in the history of the war.¹ The Battle of St Quentin Canal on 29 September 1918 broke through one of the strongest sections of the Hindenburg Line.¹⁴ Allied casualties between August and November 1918 were around 700,000; German casualties were slightly higher, at around 760,000.¹⁴

First Bulgaria accepted an armistice on 29 September 1918.¹⁵ The Ottoman Empire then signed an armistice at Mudros, with hostilities ceasing at 12 noon the following day.⁸ Austria-Hungary followed on 3 November 1918.¹⁵ A German delegation met Allied Commander-in-Chief Ferdinand Foch on 7 November 1918 in a railway carriage north-east of Paris, where the Armistice was drawn up and signed.¹⁶ Its terms demanded that German forces leave France and Belgium, surrender military equipment and U-boats to the Allies, and form democratic government in Germany.¹⁶ Wilhelm II abdicated on 9 November, and the guns fell silent at 11am on 11 November 1918.¹⁶

The Paris Peace Conference opened on 18 January 1919 and ran until 21 January 1920.¹⁵ Nearly thirty nations participated, but the representatives of the United Kingdom, France, the United States and Italy — the Big Four — dominated the proceedings.¹⁷ On 28 June 1919 Germany signed the Treaty of Versailles in the Hall of Mirrors at the Palace of Versailles; it entered into force on 10 January 1920.¹⁸ It was the first and most significant of the five Parisian treaties.¹⁵

According to French and British wishes, the treaty subjected Germany to strict punitive measures.¹⁷ Germany surrendered approximately 10 percent of its prewar territory in Europe and all of its overseas possessions.¹⁷ Alsace-Lorraine was given to France and Eupen-Malmédy to Belgium, while territory in eastern Germany was awarded to a reconstituted Poland.¹⁸ Under Article 231 of the Treaty, the Germans accepted responsibility for the war and the liability to pay reparations to the Allies.¹⁷ In 1921 the Inter-Allied Commission fixed the reparations at 132 billion gold Reichmarks, or 32 billion US dollars, on top of an initial 5 billion dollar payment demanded by the Treaty.¹⁷

The League of Nations was created, but the United States never joined it: in a final vote on 19 March 1920 the Treaty of Versailles fell short of ratification by seven votes in the US Senate.¹⁷ Further treaties followed — Saint-Germain with Austria on 10 September 1919, Neuilly with Bulgaria on 27 November 1919, Trianon with Hungary on 4 June 1920 and Sèvres with the Ottoman Empire on 10 August 1920.¹⁵ The concluding stage was the Treaty of Lausanne with Turkey on 24 July 1923, the only real negotiations with a former Central Power.¹⁵ Peacemaking took longer than the war itself.¹⁵

Casualty figures from the First World War differ by source, definition and date, so every number below keeps the definition and the date its source gives.⁶ The meaning of headings such as killed in action, wounded and casualties is misleading, and war losses cannot be calculated by nations or empires, because the main sources are army statistics.⁶ The table reproduces the US War Department figures of February 1924 as published by Encyclopaedia Britannica — 65,038,810 men mobilised, 8,528,831 killed and died and 37,468,904 total casualties — alongside the country-by-country figures and comparison estimates from other institutions.⁴

The war was a watershed.¹ It toppled four imperial dynasties, brought revolution in Russia, partitioned the Ottoman Empire, and laid the groundwork for later conflict.¹ The Sykes-Picot Agreement led to the division of Turkish-held Syria, Iraq, Lebanon and Palestine into various French- and British-administered areas.¹² The borders of the postwar mandates split up Arab lands and ultimately led to the modern borders of Iraq, Israel and the Palestinian territories, Jordan, Lebanon and Syria.¹² The Imperial War Museums judge that the settlements did not in themselves make the Second World War inevitable.⁵

The dead of the war are remembered each year on Remembrance Sunday, with a two-minute silence at 11am on 11 November.¹⁶ War memorials stand in towns and villages across the combatant countries, the Imperial (now Commonwealth) War Graves Commission cares for the cemeteries of the fallen, and the Cenotaph in London dates from 1920.¹⁶

First World War records at The National Archives of the United Kingdom are the records once held by central government departments — the British Army, the Royal Navy, the Merchant Navy and the Royal Air Force — including the departmental WO, ADM and AIR series and Field Marshal Haig's diaries (WO 256).¹⁹ As the largest repository of American World War I records, the US National Archives holds photographs, documents, audiovisual recordings, educational resources and other material documenting the American experience of the conflict.²⁰ The scholarly record continues through the international encyclopedia 1914-1918-online and the National WWI Museum and Memorial.⁶