If I remember the facts correctly, the abolitionist movement started in Europe. European countries eventually went to great expense (and risk of life) to also abolish slavery in their colonies. In many areas the move to stamp out slavery was strongly resisted and even laughed at.
In the US, it was illegal to import slaves long before slavery itself was abolished. Slave traders caught smuggling new slaves into the US were hanged, and this was actually enforced. Some framers of the constitution wanted to outlaw slavery from the start, but the southern states objected. Slavery was allowed in order for their to be a United States of America. If we’d formed two countries, let’s say a Northern United States and a Southern United States, each independent of each other, I wonder how much longer slavery would have lasted here. I’d imagine that eventually the censure and opinion of the rest of the world would have taken a toll, but it might have gone on past Abe Lincoln’s time. I’m pretty sure I read all of this in an essay by Thomas Sowell, but can’t remember the name of it. It was in his book “Black Rednecks and White Liberals.