8.2 World War I

On June 28, 1914, Gavrilo Princip, a Bosnian Serb nationalist linked to a Serbian secret society called the Black Hand, assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, in Sarajevo. Austria-Hungary saw a chance to crush Serbian nationalism and, after Germany promised full support (the “blank check”), sent Serbia an ultimatum it could not fully accept.

• July 28: Austria-Hungary declares war on Serbia.
• July 30: Russia orders general mobilization to support Serbia.
• August 1 and 3: Germany declares war on Russia, then France.
• August 4: Germany invades neutral Belgium to reach France; Britain declares war on Germany, citing the 1839 treaty guaranteeing Belgian neutrality.
• Later: the Ottoman Empire (late 1914) and Bulgaria (1915) join the Central Powers; Italy (1915) and the United States (1917) join the Allies.

Germany's Schlieffen Plan aimed to avoid a long two-front war: knock France out in about six weeks by sweeping through Belgium, then turn east before slow Russia could fully mobilize. It failed when French and British forces stopped the Germans at the First Battle of the Marne (September 1914). Both sides dug in, and by late 1914 trenches stretched from the North Sea to Switzerland.

Defense was stronger than attack. Machine guns, barbed wire and massed artillery made it nearly suicidal to cross no-man's-land. Germany used poison gas (chlorine) at Ypres in 1915, and both sides then used it. Huge offensives gained little ground: at Verdun (1916) France and Germany together suffered roughly 700,000 or more casualties, and on the first day of the Somme (July 1, 1916) the British army suffered about 57,000 casualties, about 19,000 of them killed. Tanks (first used in 1916) and aircraft were developed but did not end the stalemate until 1918.

• Eastern Front: a war of movement, with Germany defeating Russia at Tannenberg (1914). Russia's huge losses fed revolution (8.3).
• Ottoman fronts: the Allied attack at Gallipoli (1915–1916) failed. Britain encouraged the Arab Revolt (1916) and made conflicting promises about the Middle East, including the secret Sykes-Picot Agreement with France (1916) and the Balfour Declaration (1917) supporting a Jewish homeland in Palestine.
• Armenian Genocide: from 1915, the Ottoman government deported and massacred its Armenian population. Estimates of the dead commonly range from about 600,000 to more than a million, and many historians put the toll near one million. Most historians call it genocide; the Turkish government rejects that label.
• Africa and Asia: Allied forces seized Germany's colonies. Japan, on the Allied side, took German holdings in China and the Pacific and pressed China with its Twenty-One Demands (1915), a sign of its growing aggression on the Chinese mainland. More than a million Indians and hundreds of thousands of Africans served the British and French empires as soldiers, porters and laborers.

Governments took sweeping control. Britain's Defence of the Realm Act (1914) allowed censorship and control of industry; Germany's War Raw Materials Department directed scarce resources; all sides conscripted men, rationed food and spread propaganda portraying the enemy as monstrous. Women took jobs in munitions factories, transport and offices. A British naval blockade caused severe food shortages in Germany.

War weariness grew into protest and rebellion. In Ireland, republicans launched the Easter Rising in Dublin in April 1916; the British crushed it and executed its leaders, which turned many Irish people toward independence. Parts of the French army mutinied in 1917 after a failed offensive, Russia's war crisis produced revolution in 1917 (8.3), and German sailors mutinied at Kiel in 1918.

Germany's resumption of unrestricted submarine warfare and the Zimmermann Telegram, which proposed a German alliance with Mexico, brought the United States into the war in April 1917. Revolutionary Russia left the war in March 1918 with the Treaty of Brest-Litovsk. Germany's last great offensive in spring 1918 failed, Allied counterattacks pushed it back, and its allies collapsed. Kaiser Wilhelm II abdicated on November 9, and the armistice took effect on November 11, 1918. Within months, the German, Austro-Hungarian, Russian and Ottoman empires had fallen or were collapsing. Austria-Hungary dissolved into new national states, and from the Ottoman heartland Turkish nationalists created the modern Republic of Turkey in 1923. Europe's relationship with the world had shifted: the war had gone global, empires had been overthrown, and the United States had emerged as a world power.