What was the main purpose of u. s. foreign policy in the decade following world war ii?

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

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 .