>>513711385
>>513714719
>some parts are very fertile and productive, a huge chunk of it is rainforest.
Anon, rainforests aren't fertile. They're lush, but they can't support large-scale agriculture at all. The soils is heavily acidic and washed-out (requiring large amounts of charcoal or lime to make usable), their plants are prone to drowning, and all of the land has to be laboriously cleared out.
The most efficient way to use the land is by either settling a delta to use the fresh sediment that gets pushed onto your land (Kingdom of Kongo), establishing a large number of fruit trees and accepting you'll have a small, well-supported population (Uganda), or by clearing the land for use by pastoralists (Swahili).
Anyway, the diseases and isolation pose more of a problem than the soil itself since your population is capped, you don't have easy access to foreign knowledge bases, and you can't establish trade links to cover your weaknesses. Good for establishing self-governing villages, but not for building up sprawling civilizations.

For the record: The only parts of Africa with decent soil quality are Morocco, Nigeria, a small section of Ethiopia, Zimbabwe, Madagascar, South Africa, and parts of the Nile. Everything else is marginal due to either climate or soil quality. Africa hasn't seen much geologic activity recently to deposit fresh nutrients, so they use dust storms from the Lake Chad area and eroded mountain soil from the Great Lakes to farm.
>what about the savanna
Grows grass and almost nothing else in sufficient quantities. Basically a steppe.
Brits should know this, given how much of it they conquered and failed to make useful.
Most of Africa's agriculture nowadays is heavily reliant on industrial fertilizer.
>>513715056
Water access is a non-concern in that environment.