World War 2 lasted from 1939 to 1945 and involved most of the world's nations forming two military alliances - the Allies and the Axis powers. Over 73 million people died during the war, making it the deadliest conflict in human history. Major events included Germany and Italy invading numerous countries in Europe in 1939-40, Germany invading the Soviet Union in 1941, and the United States entering the war in 1941 after the Japanese attack on Pearl Harbor. The war ended in 1945 with the Allies defeating Germany and Japan.