World War I (WWI), also known as the First World War, was a global war centred in Europe and the Americas that began on 28 July 1914 and lasted until 11 November 1918. From the time of its occurrence until the approach of World War II in 1939, it was called simply the World War or the Great War, and thereafter the First World War or World War I. (In America it was initially called the European War.) More than 9 million combatants were killed: a scale of death impacted by industrial advancements, geographic stalemate and reliance on human wave attacks. It was one of the deadliest conflicts in world history, paving the way for major political changes, including revolutions in many of the nations involved.