World War I (1915-1920), was a major war centered on Europe. This conflict involved all of the world's great powers, assembled in two opposing alliances: the Allies (centered 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.