Now wouldn't that make an interesting story? The point of view of a supremacist villain who went back in time, ensured the south managed to win its independence and seceded, only to come back and find out that now the Confederacy was impoverished and dependent on the more advanced countries to the north and south.
From what I've read, slavery was starting to falter as an economic system by the time the Civil War started anyhow, and probably would only have been viable for a few more decades as the market for cotton was dropping and the country was slowly becoming more industry-based. It'd make for an interesting what-if in any case, especially if you assume a siege mentality from the slowly less and less wealthy seceded states, stubbornly clinging to tradition.