World War I (WWI) or First World War (called at the time the Great War) was a major war centered on Europe that began in the summer of 1914. The fighting ended in November 1918. This conflict involved all of the world's great powers, assembled in two opposing alliances: the Allies (centred around the Triple Entente) and the Central Powers. More than 70 million military personnel, including 60 million Europeans, were mobilized in one of the largest wars in history. More than 9 million combatants were killed, due largely to great technological advances in firepower without corresponding advances in mobility. It was the second deadliest conflict in history.