My seven generations back grandfather was the son of an Irish immigrant, who lived in Abbeville South Carolina, a small town. He was a Presbyterian minister. He preached against slavery in 1810. When that didn't go over in his neighborhood, he packed up his family and left for Ohio. Half his congregation went with him. The town they built is called Fairhaven. It's a nice drive up Ohio 177, near Miami.

Slavery happens when labor is in short supply. The first settlers enslaved Native Americans, Blacks, orphans, debtors, prisoners of war, and assorted others.
The first Black in Maryland began as an indentured servant, and ended up on the governing council. Benjamin Bannacker was the grandson of an Irish woman who married the slave she bought to work her land. Slavery on the big plantations became a hellish institution because the planters couldn't afford to think of their slaves as humans, anymore than the American who owns a factory in Calcutta can think of his employees as human.