MODERN AGRICULTURE!!!
Global Warming on Free Republic here, here and here
There are, broad brush here, basically two sorts of countries in Sub-Saharan Africa.
The larger group tended to have good natural resources and leaders who looked to the likes of Marx for inspiration.
The smaller number of nations had leaders who emulated the Brits or, if they were really blessed as Botswana was, who looked to men like Adam Smith and George Washington for inspiration.
That’s basically the dividing line. According to a Ghanan lady I know it might also be split between those leaving French rule and post-English colonial with much the same effect.