To be fair, in this case, the superior race was mostly enslaved by itself, and then traded off to Europeans for gold and other goods.
The Africans were tough guys. It shows in the fact that the Zulu tried to take on Brits who were armed with far superior technology. It would've been liked the Roman legions trying to take on men armed with cannons, rifles, gatling guns, etc. Physically they had reached peak levels for humanity, but technologically they had been isolated from the rest of the world.
It is also often forgotten that the "supreme" white Europeans themselves were emasculated and humiliated for centuries by Muslims who used them as slaves to prop up their civilizations, up until the 19th century. No race has really escaped the cruelties of enslavement, either by their own hand, or by someone else.
I don't think there's any point in having an inferiority or superiority complex at this point, about slavery, when we know that pretty much every race went through that process. It's not really an exclusive club that any particular race belongs to.
