World War II
World War II was a global conflict that lasted from 1939 to 1945. Eventually all countries became a part of two military alliances: the Allies and the Axis. WWII was marked by such events as the Holocaust and the first instance of the use of nuclear weapons in warfare. Because of the scope of WWII, the major powers participating in the war placed their entire economic, industrial, and scientific capabilities at the service of the war effort.