World War II was a global conflict from 1939-1945 that involved most nations splitting into two opposing military alliances: the Allies and the Axis powers. Key causes included the Treaty of Versailles, the rise of fascist regimes in Germany, Italy and Japan, and their subsequent aggression that violated international agreements. Major events included Germany's invasion of Poland starting the war, Germany and Italy's rapid conquests in Europe, Germany's invasion of the Soviet Union, Japan's attack on Pearl Harbor drawing the US into the war, the Allied invasions of German-occupied Western Europe on D-Day, and the US dropping atomic bombs on Hiroshima and Nagasaki to end the war. Over 60 million people died making it the dead