The South would have ended slavery in time as well. Slavery was dying all over Europe. That's the only reason Britian and others did not help the south. Robert E. Lee was against slavery, he was fighting for his homeland. Lincoln set a horrible example by invading the south and making it be part of the Union. The old Soviet Union and others used Lincoln as reason to keep their territories from breaking away. US complained about that but it had no problem with Lincoln doing it.
Southern forces fired the first shots on supply ships that were arriving to replenish Ft Sumter. The South started the Civil War.
When? Slaves were continuing to appreciate in value throughout the first half of the 19th Century. They were the greatest capital holding in the south, exceeding land. The machines and chemicals that eliminated the need for extensive hand labor in cotton cultivation weren't developed until the 1940s. Is that when the south would have ended slavery?
When, and how did anyone at the time know that? Slave prices were at all time highs before the war. It sure wouldn't have appeared to anyone in 1860 that slavery was on the way out, and I can't recall of anyone at the time, North or South, predicting it would just go away on it's own.
Lincoln believed if slavery could be contained in the states where it existed, not allowed to expand to the west or into Mexico or Central America, it would choke on itself. Most southerners believed if it were contained where it existed, they would eventually be hopelessly outnumbered by slaves, their wealth would vanish, and they would face the fate of the French colonials in Haiti. They looked to expand their system to the West and South.
The Republicans and Lincoln opposed expansion. The Slave power saw expansion as critical to their survival. They were positions that evolved over a period of decades as the nation grew, not something that suddenly sprang out of the blue in 1860. They were diametrically opposed core beliefs which invariably leads to conflict.
Slavery was dying all over Europe.
Study some history. Europe never had much in the way of a slave system. They had peasants --- far more than they needed, (hence massive immigration to the US, Canada, Austrailia, South America etc.) Those peasents were locked to the land and the royalty, or their cronies, owned all the land, or at least the land that was worth owning. There was no need for imported slaves although the system, minus the high demand for labor, was virtually identical to the American plantation system.