Egypt had the Nile River with its rich farmland and, more importantly, the Mediterranean Sea. Natural Resources and access to trade — a winning combination for prosperity.
Sub-Saharan Africa had few navigable rivers or ocean harbors. They were screwed.
Have you read “Guns, Germs and Steel”? by Jared Diamond?
The sub-saharan Africans - of which there are 3 races:
1. Khoi-san (bushmen)
2. pygmies
3. bantu speakers
all had it great before the end of the last ice age in 10K BC — they had food plenty and warmth. The rest of the world was a frozen spitball (I exaggerate), but they had it good.
The same for the Aborigines in Australia and then the early migrants to the Americas.
But later, with the agricultural revolution, things changed.
I liken it to the sea-change in European countries’ fortunes after 1492 and 1495 — until that point in time the countries on the Mediterranean basin like Genoa, Venice etc. were rich. But then the Atlantic facing countries got rich