Slavery is FANTASTICALLY simplistic. One person owning another and profiting off of his labor is wrong. Period. Full stop.
White people ended a situation they created. Slavery only became a profitable business in Africa because white people were paying top dollar for slaves. The economy of the Congo eventually became entirely based on the slave trade to the point where it had no other industries, then it was taken over by the Europeans in a way that was slavery in all but name.
Let's be blunt. White people are kind of awful. We need to be better.
Try to focus, buddy, White America doing something fucking evil isn't excused because somewhere else in the world, someone might have been doing something similar.
Debt Peonage was a system created in the south to return black people to slavery by inventing crimes such as "walking along the railroad tracks" and then putting people into servitude for years by generating debts they could never pay back.
The practice wasn't outlawed until 1942, and only then because we didn't want Nazi Propagandists to use it against us.