You can argue which act of war started the war but it seems like it would make sense form a logical point of view to go with the first act of war. I would argue that allowing people to use your country to train and plan attacks on another country is an act of war and the Taliban was the government at the time. Also technically the resumption of violence following the violation of an armistice agreement is really the same war even if it is a decade later.

If anything post war Japan went easier than Germany. The Japanese Emperor agreed to get behind the rebuilding if we agreed to not try them for war crimes that were in some ways worse than what happened with the Nazis and the Japaneses embraced the changes that brought. Most of the Japanese manufacturing and quality process that are so talked about today were created by Americans sent over right after the war. Also MacArthur had almost half a million troops to keep the peace with.