When you get down to brass tacks, slavery is the result of which can best perform -- albeit involuntarily -- the labor that is required. And most of that required work is plain old pick-and-shovel labor.
A quick example: In the early years,the Spaniards, in the new world (South America) discovered silver, and, to a less extent cane sugar. They did not want to work these themselves. The aborigines were to a point fair-to-poor slaves, generally lacking the stamina needed/demanded by the Spaniards. Hence the importation of negros, who were far more able to carry out the work required.
IOW, blacks became slaves -- the preferred slave stock --in the New World simply b/c they filled the need. It wasn't any "racist invention".
Actually, Blacks themselves didn’t make for good slaves, but rather, Western Africans made for great slaves. Western Africans tend to be stockier, larger, and stronger than Eastern Africans, much like how Germans tend to be larger than Frenchman but are both still white. Case in point, Barry’s daddy’s VERY slim and slight, but Hakeem Olajuwon is huge.