Slaves never build anything. Which is why sub-Saharan Africa has no great ruins. It's also why niggers have never built a modern, complex civilization. They are not smart enough. Their intelligence level is too low, collectively. When you are building a civilization, collection intelligence matters. It isn't enough that one or two men are geniuses. You need a whole lot of very bright men and women working together. Black Africa never had that, and they still don't have it, because their lack of intelligence is genetic. They are a sub-species of humanity with significantly lower intelligence than the rest of us.