World War I, or the First World War (often referred to as WWI, WW1, The Great War and The War to End All Wars), was a global military conflict which involved the majority of the world's great powers, organized into two opposing military alliances: the Entente Powers and the Central Powers. Over 70 million military personnel were mobilized in the largest war in history. In a state of total war, the major combatants placed their scientific and industrial capabilities at the service of the war effort. Over 15 million people were killed, making it one of the deadliest conflicts in human history.