US provided army and weapons to go against Germany, assisting the allied power to help gaining back the liberation of France on D-Day for example.
As for Japan, after the Pearl Harbor Incident, the US joined the war, defeating the Japanese in the sea battles in pacific. US also finally lead to the withdrawal and the end of WWII by dropping atomic bombs on Hiroshima and Nagasaki.
Hope it helps!
The largest difference is in the main course lunches.
