I think the South had a golden window of opportunity to win the war on one occasion: immediately following Bull Run, the first large battle of that war. The Union Army fled in panic at the conclusion of Bull Run, and there was effectively nothing standing between the Confederates and Washington. Had they moved without hesitation and occupied Washington, they could have dictated terms to a stunned Union. They could have secured Southern independence at that moment, and with very minor loss of life on both sides.

Even as it was, many in the North were calling the war "lost" in the panicky days following Bull Run....but the South did not move decisively to capitalize on the situation. They were content with simply winning a tactical victory on the battlefield.

They should have gone straight for the jugular, and they could have. If they had, Lincoln's presidency would have gone down in ruins, and there would have been 2 American nations after that, not one.

And in that case....there probably would have been some further wars between those two farther down the line. What that would have led to is impossible to say. They would certainly have gotten into loggerheads over western expansion into the territories and various other issues as time went by.

The smartest thing the South could have done, had they secured independence, would have been to work for a close alliance with the British Empire, thus hemming the North in between themselves and Canada. ;-) It would have served the interests of the South and Great Britain quite well to do that, and it would have profoundly changed the history of the entire world in the process.

As for slavery, that was an institution that wouldn't have lasted much longer in any case. It was on the way out.