World War I, or the Great War, was a global war, centred in Europe, that began on 28 July 1914 and lasted until 11 November 1918. It involved all of the world’s great powers, which were assembled in two opposing alliances, the Allies (Great Britain, France and Russia) and the Central Powers (Germany and Austria-Hungary). These alliances were both reorganised and expanded as more nations entered the war: Italy, Japan and the United States joined the Allies, and the Ottoman Empire and Bulgaria the Central Powers. Ultimately, more than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history.
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