I have a different theory from 1st hand experience.
The problem with Africans is that they have a tribal identity> national identity. They are also VERY superstitious.
Let's say you go to Africa and teach a small group of them how to farm/ any skill.
They would be BRUTALLY MURDERED by the tribes who didn't and they would justify it with some superstitious BS.
This is pretty much African history in a nutshell and that's why they can't progress.
@basedbagel @37712 Explains why the Zulus would just wipe out other tribes rather than attempt to conquer or enslave them.