World War I Begins
World War I, fought between 1914 and 1918, was one of the deadliest and most transformative conflicts in human history. Triggered by the assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, it drew in the major powers of Europe and many of their colonies and allies, killing millions of soldiers and civilians and redrawing the political map of Europe and the Middle East.
The war's roots lay in decades of rivalry among the great powers. Europe was divided into two main alliance blocs: the Triple Entente of France, Russia, and Britain, and the Triple Alliance of Germany, Austria-Hungary, and Italy, though Italy stayed neutral in 1914 and later joined the Entente. Naval and colonial competition, an arms buildup, nationalist movements in the Balkans, and the weakness of the Austro-Hungarian and Ottoman empires all heightened tensions. Historians still debate how much responsibility each state bore, and the question of war guilt remains contested.
On 28 June 1914, Franz Ferdinand and his wife Sophie were shot in Sarajevo by Gavrilo Princip, a young Bosnian Serb nationalist. Austria-Hungary, with assurances of support from Germany, issued a harsh ultimatum to Serbia and declared war about a month later. Russia mobilized in support of Serbia, Germany declared war on Russia and France, and Germany's invasion of Belgium brought Britain into the conflict. The Ottoman Empire joined the Central Powers in late 1914, and the war spread across Africa, the Middle East, and Asia.
On the Western Front, the German advance was halted in France, and the fighting settled into trench warfare stretching from the English Channel to Switzerland. Battles such as Verdun and the Somme produced enormous casualties for small territorial gains. New technologies, including machine guns, heavy artillery, poison gas, tanks, and aircraft, shaped the fighting. The Eastern Front was more fluid, and Russia's collapse amid revolution in 1917 led to its withdrawal from the war. That same year, the United States entered on the Allied side, partly in response to German submarine warfare.
Fighting ended with the armistice of 11 November 1918, after Germany and its allies had been worn down by military defeat and internal strain. The Treaty of Versailles and related settlements dissolved the Austro-Hungarian, Ottoman, German, and Russian empires, created new states, and imposed heavy terms on Germany. Many historians argue that the unresolved grievances and economic turmoil that followed helped set the stage for World War II. The war also reshaped societies through mass mourning, women's expanded roles in the workforce, and a lasting skepticism about national glory.