The Confederates ran a concentration camp called Andersonville (read the book) that killed many POWs The German prison camps had a much lower death (Deaths per 1000 among those who signed the Geneva Conventions) rate than the Confederates at Andersonville or our current buddies the Japs.
We hung The Confederate commander, lots of Japs and a few Germans.

As one German historian said: "Had Hitler dropped dead in 1938, he would be considered one of the major successful leaders of the 20th Century."
He pulled his country out of the depression w/o firing a shot. FDR needed WW II to get us out.

War is Hell and a civil war is the worst of wars.