The consensus among the scholars I've read is that the South may well have won - even a sustained stalemate would have constituted a victory - had it managed to break the blockade and establish commercial relationships with the European industrial powers of the time, specifically Britain. Cotton was still, in the 60s, sufficiently in demand to provide the cash necessary to offset much of the North's advantage in material; all that was lacking was the logistical chain necessary to provide it to the front.
Politically Europe was in an interim period at the time between the revolutions of 1848 and the Bismark/Napoleon III period. Whether a sustained European military intervention would have been possible is less certain, probably not on land where it was less necessary, probably so at sea courtesy of the Royal Navy, where it might have made a real difference. It was that last piece that constituted a real Northern diplomatic victory and probably shortened the war considerably. All IMHO and subject to (intense) debate, of course...
Simlar to how French aid helped us in the revolution.
In reality, I think the South could never have won a clear victory. The Civil War was the first modern war, and it's clear that the South did not have the wherewithal -- people, resources, and industry -- to properly fight it, whereas the Union did.
Let's be quite clear: the North flat out won the war, and the South flat out lost it.
The only "victory" the South could have won is an armistice born of war-weariness on the part of the North. I think however, that the war would eventually have started again, for the same reasons, though probably more in the west. And the South would have been defeated by the North, for the same reasons.
Ok, but that's like saying if the Germans could cross the English Channel in July 1940 they would have defeated Britain.
Both are true but neither the South nor Germany had the Navy that was needed.