Succinct.
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...
Succinct, but not true. Gettysburg is a prime example. In each and every battle, victory on either side was determined by the better general combined with the state of his troops moral and confidence. Early in the war this fell mostly to the Confederates. Later, as the Union fielded better Generals and the troops gained confidence in them the tide swung.