Some refer to Japan as America's Great Britain of the east. Japan's Emperor and Navy opposed the belligerent Army as it embarked on empire building leading up to WWII. After WWII America found it convenient to continue to use Japanese bureaucrats to administer Indochina and surrounding areas, which caused resentment among native populations.
I think that FDR and Truman were better in foreign diplomacy, we may have had Japan as allies against the Nazis. But hind sight is 20/20. The important thing now is to include as much positive discussion and action to keep a strong and growing friendship with our Japanese Allies.
You're right about continuing Japanese administration on demilitarized former Japanese conquests. The Koreans were particularly resentful and distrustful of Americans who only bothered themselves to use the Japanese administration.
(Did you know that the US Marines fought Koreans in 1871? It was our first real contact with Korea?)
The USS General Sherman Incident:
http://www.globalsecurity.org/military/ops/sherman.htmhttp://en.wikipedia.org/wiki/General_Sherman_Incident The Battle:
http://www.shinmiyangyo.org/http://en.wikipedia.org/wiki/Shinmiyangyo
But if post-WW2 Congress and Presidency took seriously the Communist threat like they should have, the US Soldiers in Korea would not have had to use WW2 Japanese military intelligence to defend themselves from the North Korean attack. Post WW2 national defense and foreign diplomacy fell to complacency.
Checking my historical notes...yep, FDR and Truman--both Democrats.