What was the main purpose of U. S. foreign policy in the decade following World War II?

Foreign policy was we don't intervene in Europe says the one document I cant put my finger on

until World war two

all because of Japan we were involved in all conflicts out of the western hemisphere.

Also on a side note.

America would not exists any more if Japan didn't attack us also if Germany

did not attack Russia.

The main purpose was t o prevent communism from spreading to new countries.