The First World War, also known as the Great War and in the United States as World War I, was a global military conflict that embroiled most of the world's great powers, assembled in two opposing alliances: the Triple Entente and the Triple Alliance. More than 70 million military personnel were mobilized in one of the largest wars in history. The main combatants descended into a state of total war, directing their entire scientific and industrial capabilities into the war effort. Over 15 million people were killed, making it one of the deadliest conflicts in history. The proximate cause of war was the assassination on 28 June 1914 of Archduke Franz Ferdinand of Austria. Soon after, a system of alliances were activated that would see Europe at war. The Western Front saw the largest concentration of Commonwealth troops with soldiers occupying sectors of the line from the North Sea to the Orne River.