World War I (WWI or WW1), also known as the First World War, was a global war centred in Europe 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, 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 casualty rate exacerbated by the belligerents' technological and industrial sophistication, and tactical stalemate. It was one of the deadliest conflicts in history, paving the way for major political changes, including revolutions in many of the nations involved.