"World War One", "Great War", "WW1", and "WWI" redirect here. For other uses, see World War One (disambiguation) and Great War (disambiguation). For the album by White Whale, see WWI (album).

World War I (WWI or WW1), also known as the First World War, or the Great War, was a global war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918. More than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history. Over 9 million combatants and 7 million civilians died as a result of the war (including the victims of a number of genocides), a casualty rate exacerbated by the belligerents' technological and industrial sophistication, and the tactical stalemate caused by trench warfare, a grueling form of warfare in which the defender held the advantage. It was one of the deadliest conflicts in history, and paved the way for major political changes, including revolutions in many of the nations involved.