World War I, which was predominantly called the
World War or the
Great War from its occurrence until 1939, and the
First World War or World War I thereafter, was a
major war centred in
Europe that began on 28 July 1914 and lasted until 11 November 1918. It involved all the world's
great powers,
which were assembled in two opposing alliances: the
Allies and the
Central Powers.
These alliances both reorganised, and expanded as more nations entered the war. Ultimately more than 70 million military personnel, including 60 million Europeans, were mobilised in one of the largest wars in history.
More than 9 million combatants
were killed, largely because of great technological advances in firepower without corresponding advances in mobility. It was the sixth-
deadliest conflict in world history, subsequently paving the way for various political changes such as revolutions in the nations involved.