That is all true. Slavery was a consistent, standard part of civilization for thousands of years. Every major ethnic group has been slaves and has enslaved. Blonde Finnish women were prized by African and Middle East Sheiks and Mullahs.

But the slavery of the Americas (heavy in the Carribean, beyond the US) had a particular stink to it. Africans were hunted and captured because they were considered to be less human than other ethnic groups (often captured and sold by other Africans). But beyond that, after they were freed they still could not achieve true freedom because of Jim Crow laws. That is why reparations are particularly appropriate in this case.