What would have happened if the southern states had won the civil war?

If the southern states had won the civil war, we can reasonably expect that the Confederacy would still exist to this day, and the United States of America would no longer include those states which seceded during the war. Whether slavery would still be practiced in the Confederacy even in the 21st century, would be hard to say. Even without being defeated by an abolitionist North, the Confederacy could still have produced its own reform movement at some time, particularly since modern agriculture can be done even more efficiently with the help of modern farm machinery such as a combine harvester, than it can be with slave labor. The history of the world in general could have been very greatly affected, since the US was a major factor in the outcomes of both WW I and WW II. Perhaps the reduced US would not even have entered WW I and the war would have had a different outcome. But all of that is very speculative. We have no way of knowing for sure how things would have worked out.