Definition
World War I, also called the Great War, was a global conflict fought from 1914 to 1918, principally in Europe but with theatres in the Middle East, Africa, and at sea. It pitted the Allied Powers — led by France, Britain, Russia, and later the United States — against the Central Powers of Germany, Austria-Hungary, and the Ottoman Empire.
The war was triggered by the assassination of Archduke Franz Ferdinand of Austria-Hungary in June 1914, but its deeper causes are often summarised by the acronym M-A-I-N: militarism, alliances, imperialism, and nationalism. A web of mutual defence treaties turned a regional crisis into a continental, then a worldwide, war.
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The Western Front settled into a line of opposing trenches stretching from the North Sea to Switzerland. Soldiers lived in mud, disease, and constant artillery fire, while offensives across the deadly no man's land cost hundreds of thousands of lives for a few kilometres of ground.
The war ended when the Central Powers collapsed under blockade, exhaustion, and the arrival of fresh American troops. An armistice took effect on 11 November 1918. The 1919 Treaty of Versailles assigned Germany sole war guilt, imposed heavy reparations, and created new states from the fallen empires.