But there's no evidence suggesting that either factories or machines would have ended slavery, just the opposite.
By 1860 slaves were working in factories and operating machines of that day, nothing suggests they could not have continued so indefinitely.
Had there been no Civil War, or had Confederates won it, then slavery itself, that "peculiar institution" would have seen (to pervert Lincoln's famous words):
Today we imagine Southern slavery in 1860 was dead or dying, but nobody at the time believed that.
God made us all free.
The point that was attempting to be made was that many people have done fer better here than if they’d been left on the other continent. The horror stories from the day were the exception, not the norm.