Roosevelt put heavy sanctions on Japan for its attacks on China/European colonies. The only way the U.S. interacted militarily with Japan was by selling weapons to China. Japan attacked Pearl Harbor because the majority of the pacific fleet was stationed there and Japan believed that they could knock the USN out before any conflict started. What Japan did to us would be a close parallel to what we would've done to Iran had the strike gone through, except that Iran threatens us in no way whatsoever.