The u.s. DID get involved.
yes they were
No
World War 2
the US by FAR.
December 8, 1941 was the date of the US declaration of war
The US was involved for 6 years from 1941-1945
The United States became involved in the World War II about March 1941.
Japan
the USSR and the US
Dec 7, '41.
The US contributed some 16 million personnel to the Second World War. I'd say that would indicate they did get involved.