If Lee was a sociopath, so was every other general. That’s what command is - sending men into battle knowing some of them will die.
As for 1940....had the US not intervened in the first world war and tipped the balance in the Entente’s favor, it almost certainly comes to a negotiated settlement. Both sides were exhausted. No Versailles and no Triannon Treaties and Imperial Germany is left intact with the constitutional monarchy still intact. Hitler then is politically impossible. The Hapsburg Empire remains intact. An enormous power vacuum is not created in Central/Eastern Europe that Germany or the Soviet Union was guaranteed to fill. WWII simply does not happen - nor does the holocaust.
So if the Southern states had left, would the remaining rump US have intervened in WWI? It would have been nowhere near the power it was with about 1/3rd of the land and population gone. It might’ve stuck to a more modest foreign policy as it had generally had prior to its entry into WWI.
Ever read Harry Turtledove? He actually explores that stuff in his “alternate history” novels.
In one, because the south won the civil war, the entire continent split and the result was that during WWI the north supported Germany and the south supported France/England. There was an American front.
By far, his best book is Guns of the South. A bunch of South Africans from 2015 go back in time and start off by, right after Gettysburg, give Lee 100,000 AK 47’s. The impact on individual battles as well as the “secret” response of Lee is a fascinating read. There is one great line where the “riverton men” (the guys from the future) have these simply amazing rations that Lee and others are mesmerized by. They’re called “Cup-o-noodles”. :)
His later books are in multiple volumes and cover post-civil war, WWI and even WWII. In WWII we are invaded by aliens in 1942 (IIRC) and suddenly everybody is working together - sort of. It was interesting but after a while I felt like I was being strung along, as is done in so many modern TV shows.