[HoneyBadger]

B0rsuk, did you get my PM?

And one of the reasons African slaves were so popular in America, was actually because of their skin colour. As suggested above, they were instantly recogniseable as atleast potential slaves, which made them a lot easier to recapture, if they tried to escape. And being from Africa, they would have little support system (atleast until the abolitionist movement started taking off), if they did manage to escape successfully.

There were white slaves in America, and many more "indentured servants", who were more or less temporary (for up to a decade or more) slaves-by-contract. The Spanish had also enslaved the natives of South America, but so many died, or escaped (a lot easier to run for the nearest mountain, than to swim to Africa, although many African slaves did escape to join Native American tribes).

It was also probably a little easier for some slaveholders to ignore and stomach the horrors of slavery, if you were inflicting it on someone so clearly foreign.