Well, Germany was captured by the Allies. The US owned West Germany and the Soviet Union owned the East Half. This is what eventually led to the Cold War.
1941
they were a allie.
How_did_the_us_involvment_in_World_War_2_escolate
1945
Supplying Allies with weapons
The Japanesse surrender.
Self defense, the US was attacked.
The US is not yet involved in world 11. The next world war should be WWIII so they have a way to go.
December 7th 1941
US involvement was tremendously helpful to the Triple Entente; it is likely that the outcome of the war would have been different had the US not gotten involved, either a victory by the Central Powers, or at least a stalemate, which would have resulted in a very different peace treaty than the Treaty of Versailles. This would have had huge historical consequences of various sorts.
The US entered World War 2 after the attack on Pearl Harbor. When over 2,400 US lives were lost in a sneak attack on a Sunday morning, there was no stopping US involvement in the war.
World War I was from 1914 to 1918, US involvement was 1917 to 1918.