If you want to try Sherman for war crimes, I have a charge that might stick--but it is "ex-post-facto."
I have read that Sherman forced Confederate PoWs to remove landmines emplaced by Confederate forces. Under the modern Geneva Conventions, this is specifically forbidden. But land mines were a new "infernal" weapon in that era. No one had codified the rules on them.
Probably more like IEDs than landmines. Another Civil War military invention that is alive and well in the modern day.
I googled that and got this:
This title is pretty misleading and implies that Sherman was marching them around to clear the mines by stepping on them...
But if you actually read the link, you'd see that after the Union took the fort. He basically was like, "you guys planted them, now you guys gotta dig em up".
If so, it wasn't any war crime.
Slightly off track, I saw a movie recently, a Danish film called "Land of Mine". It was based on true facts that after the Second World War the Danish government kept German POWs and forced them to clear land mines before letting them go back to Germany. Thousands were killed. That's not too far from what Sherman did.