(1914-1918) a war in Europe fought between France, the UK and its empire, Russia, and the US on one side ('the Allies'), and Germany, Austria-Hungary, and Turkey on the other side. The war started as a result of the murder in Sarajevo of the Archduke Franz Ferdinand, a member of the Austrian royal family. World War I was fought in many different areas, but for British people the strongest image is of the 'Western Front' in Belgium and northern France, where the armies of each side lived intrenches (=long deep holes in the ground), with an area called "no-man's land" between them. Many of the famous battles on the Western Front ended without either side gaining much land, and the names of these battles especially the Somme, Passchendaele, and Ypres, have come to represent the way that millions of young men were killed for no very good reason. For people from Australia and New Zealand, the battle of Gallipoli, where thousands of their soldiers were killed, is remembered with great sadness.
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.
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