It depends on whether you want them to behave as a conquered nation with generations of resentment or as an ally and equal partner. I MUCH prefer the later.
Do you really think the union would NOT have not the war without the depravities which characterized Sherman's march?
And, by the way, I think Lincoln was one of our greatest presidents. I would rank only Washington, Jefferson and possibly Ronald Reagan ahead of him.
But I also think his two greatest mistakes were:
I would too, but it's a faulty premise. There would never be two self-sustaining nations. The south simply could not stand on its own. It lacked the infrastructure and the resolve to build the infrastructure necessary to provide for itself.
Besides - how much faith can one have in a confederacy built on the notion that when the times get rough the rough get going? If you base your culture on secession, why wouldn't you expect secession to be a permanency in your life?
This argument does not seem to apply very well to Japan and Germany, whose cities we burned without thinking about dallying on our way to unconditional surrender. The waring parties succede best post bellum when the victory is clear.