If you look at Africa, North Africa developed rapidly under the Egyptians and Phoenicians, and only failed under islam.
If you look at west africa, it sure looks like civilization should have taken off there, and the only thing I can see so far is (a) limited productivity of the territory meaning high cost of administration, (b) lack of eurasian or south american domesticated animals and vegetables, (c) painful disease gradients, and (d) isolation from trade once they reached sufficient scale, that they needed eurasian technology from others to continue scale. I’m just too ignorant still to understand. But it looks like a ‘Jared Diamond’ argument there.
If you look at east africa, the two red sea routes (the isthmus across the south, and the river at the north) this territory was ‘hostile and unexplored’ and the trade route poorly usd until roman times (and was prime booty for islam).
If you look at the territory between east and west africa, and between east africa and the highlands of southern africa, these regions are just too costly to transit for trade – especially in comparison to the mediterranean. I mean, geography is just … damn, africa is HUGE.
The route across the isthmus like that between alaska and siberia was walkable or at least open to simple migration out of africa. The semitic peoples (i think) developed out of west eurasians on this land bridge route, then moved north, and once the semitic peoples developed they migrated southward and established kingdoms in the horn of africa. (the one that is now slowly splitting off of africa to form a large island as big as the british isles.)
Even once horses were introduced, the climate is not beneficial for raising horses (especially compared to mongolia or the european plain).
Trade tended to round the west coast rather than cross the center. Meaning that trade with west africa was prohibitively distant until the age of sail.
—“cavalryman in West Africa ultimately lost out to the musketeer. Firearms were not only, eventually, a more efficient arm of warfare: they were also very much cheaper than horses. The same happened in Asia, of course: but perhaps not quite so inevitability. For a very long time firearms were inferior both in range and rate of fire to the Turkish compound bow. The Tatars of the Crimea were still, in the seventeenth century, raiding effectively in Eastern Europe against the opposition of field artillery and troops armed with muskets. And western writers on Ottoman expansion have tended to lay too much emphasis on the Janissaries – infantry musketeers – as against the Ottomans’ more significant light cavalry. But gunpowder had nevertheless sounded the death-knell of the mounted archer’s invincibility. In West Africa the heyday of the cavalryman lasted for a much shorter period than in Asia – not more than five centuries”—
Still have to study each of these west african empires, because it sure looks like there was sufficient mass there.