The Second World War occurred between 1939-45 under US Presidents Franklin D. Roosevelt and Harry S. Truman terms in office. The United States became involved after Japan bombed Pearl Harbor in Hawaii and Roosevelt declared war on December 8, 1941 primarily against Japan but also the axis powers as whole. The Axis powers were Japan, Germany, and Italy and they were against the Allies were Great Britain, the Soviet Union, and the United States. The main leaders for the axis powers were Adolf Hitler, Benito Mussolini, and Emperor Hirohito. Throughout the war the United States’ goals were to stop Japan from expanding in the South Pacific and help Great Britain and the Soviet Union against the Nazis of Germany.
The United used both Isolationism and Collective Security for their foreign policy in World war 2. They used both because at first they did not want to be involved because they thought the WW1 entry was a mistake and did not wish to be dragged into European affairs again. When Japan attacked Pearl Harbor though, the US had no choice but to become involved and join the Allies to also combat Germany and Italy.