I answered a similar question to this a couple of years ago. You can find my response here: https://www.reddit.com/r/AskHistorians/comments/6tios5/why_were_there_no_nuremburgtype_trials_for/

Happy to answer any follow up questions.

Here is answer that deals with why Confederate leaders were not tried for treason by u/ReadySettGo with follow ups by u/Rittermeister and u/dandan_noodles