Now you are beginning to sound like a 1619 Project type, since if there weren't slaves, there wouldn't have been a political compromise to keep slaves at the founding of the US, the Civil War, the 14th amendment, etc.
The "horse" is the civil war. It is not the advent of slaves.
Slavery was going to die out anyways. It was declining even in the South. Land was getting farmed out and there was no new territory into which this sort of farming could expand.
People who think the civil war was about slavery have simply been misled by the propaganda still emanating from that war. But for those who believe that slavery was the cause, the evidence indicates it was going to wither and die in a matter of time anyways, so the war was unnecessary.