Why was Tojo hung for war crimes and not Hirohito?
I think there are two major reasons. The less important one is that Tojo’s participation in crimes against humanity was very easy to verify, while Hirohito’s supporters claimed he had no real authority to set policy (whether or not this was actually true). The much more important reason was that it was very helpful to maintaining a peaceful occupation of Japan to allow the Emperor to remain on the throne and instruct him as to public statements and the approval of U.S. drafted legislation.