Sherman was war criminal he was just a war criminal for the winning side. He was a war criminal not only but todays definition but by the definition of his own time. If he had been captured they would have hung him, they may have given him a trial first but then again maybe not.
By your argument we should have stood by and watched Hitler exterminate the Jews while he rolled over Europe and let Japan conquer all of Asia and enslave half the world. I know there is the argument that Japan attacked us but that argument is weak and only works if you burying your head in your ass and refuse to admit we poked them with a sharp stick until they bit back. We lost a lot of really good men we shouldn't have because isolationist had kept us from acting. If we hadn't waited to build our military and held the Philippines and the South China Sea the war in the Pacific would have been much shorter and a lot less bloody.
The world will always have super powers and the choice right now is us and China. You don't have to look at China long to know what a nightmare that would be. What is the point of being a super power if you just look at the rest of the world and say not my problem? Isolationist super power doesn't work.