Slavery would have died because of economics. The same way as the Mule was replaced by the farm tractor, because the tractor didn't have to be fed hay during the winters. And the sharecroppers were replaced by the cotton picker and the combine. Wealth often changes forms. What was wealth in 1860, becomes a burden in the 1900's.
Slavery today exist only in undeveloped countries where cheap labor is needed, because it is cheaper than the alternative. Factories build where the land is cheap, taxes are low, and the labor can be paid .50 cents an hour, rather than a dollar an hour. While a slave is not paid a wage, you still have to feed, cloth, house and provide medicine for him, or go buy another when your slave can't work.
The factory worker you don't need to worry about his needs. He is not your concern. You only have to pay him a wage. And you can hire another as cheaply as the workers who leave.
Simple natural forces of economics. If there is no profit in owning a slave, there is no logic to own a slave. They are a burden on your resources.
"The balance of power in the two houses of government, was always a point of contention and seemed to work to entrench political positions as well as sectional paranoia."
And a situation that was created by an unnatural Compromise, in the 1820 and 1850 Missouri Compromises on the admission of States to the Union, which was declared Unconstitutional by the Dred Scott ruling in 1854.
This is where man's political tampering with David Upton's "Natural Progression forces" comes into play. Had the practise of Slavery been allowed to live or die on it own merits, it would have died and there would have been no ACW.