Why was America reluctant to join the Allies in World War II?

The approach of another world war caught the U.S. largely unprepared. Having just emerged from the Great Depression, there was little time to recruit and train a military, which the nation preferred to avoid. However, the threats from fascism and communism made modern military and technology necessary. The adjustments made during World War II left the U.S. as a superpower afterwards, both economically and militarily.