The consensus in these parts is the South couldn't realistically have a) beaten the North or b) stuck around for very long as a cogent country even if they had. Using whatever tools you see fit (apart from ASBs, obviously), create a situation whereby the continental US as we know it today is made up of at least two countries that derive from the United States of America, with the latest possible POD.
In other words, create a secession scenario that's sizeable, lasting and feasible.
In other words, create a secession scenario that's sizeable, lasting and feasible.