It can be argued that anything done to shorten an evil war is justified. But I'm torn by that.
Here's a hypothetical: Suppose in 1863 Lee had chosen to go for Pittsburgh instead of Gettysburg. And let's suppose he was able to capture Pittsburgh.
Now, Lee certainly would have been morally justified in burning Pittsburgh's foundries. those foundries made cannon for the Union army. But would he have been justified in killing all the skilled civilian foundry workers?
Certainly that's a very poor parallel with WW II. But I wonder...your thoughts?
War is the absence of law, so there are no crimes. It is about killing people and breaking things. There is no such thing as a “war crime”, no matter what the liberals claim.
However, to your hypothesis: When the war is over, if you acted badly beyond expectations then you might find the enemy is still very will alive. Either you kill everyone or you try to limit your actions so that the result can be peace.
Would that Lee and Forrest might have structured more of their Army around the “Grey Ghost” model. Not that the South would have necessarily won the war, but would have made it even costlier to the North.
That being said despite my Southern sympathies, Sherman was quoted as having said, “War is the instrument our enemies have chosen. And I say, let us give them all they want.”
The Civil War is a little different since the enemy is a fellow American. I was mostly thinking of foreign wars with countries like Germany, or enemies like radical Islamists. I might be tempted to spare fellow Americans and just blow up the buildings.