I agree that Lee, Grant and Lincoln were three great Americans who came out of the war. I'd add a fourth in General Sherman. He fought a hard war, but it was what was needed to end the bloodshed and preserve the Union. He showed the spirit of magnanimity to his Southern brothers by his generous terms to Joe Johnston. Sherman gets a bad press by many, but he was only a hard soldier and was not motivated by the anti-Southern hate that characterized Sheridan.
I agree that Sherman was up there. After all, there were many great leaders on both sides of the conflict. I feel that the first three I mentioned were the most crucial. Of course, it had to do with their position as well as their character.