USA

Franklin D. Roosevelt

FDR was president of the United States at the start of WWII. His goal was to make America the "Arsenal of Democracy" which would supply munitions to the Allies but officially remain neutral. With strong national support, FDR made war on Japan and Germany after the Japanese attack on Pearl Harbor. He passed away before the end of the war in April 1945.

Harry Truman

Truman succeeded to the US presidency after the death of FDR in April 1945. While Germany surrendered a few weeks after Truman assumed the Presidency, the war with Japan was expected to last another year or more. Truman ordered the first use of atomic weapons against Japan, intending to force Japan's surrender and spare American lives in an invasion.