After taking a look at that article, there's a few flaws with your argument. In regards to your first part about them building a good civilisation, seeing as they were white colonists they would obviously know how to build in a similar style to the states back in Europe. To the next point about it being very fertile, if you take a look here you'll see the following:
As i'd states earlier, the African climate lays on the extremities of the scale with the more moderate climates simply being hard to sustain a population on since they lack the necessary rainfall.Climate
The climate of Africa ranges from tropical to subarctic on its highest peaks. Its northern half is primarily desert or arid, while its central and southern areas contain both savanna plains and very dense jungle (rainforest) regions. In between, there is a convergence where vegetation patterns such as sahel, and steppe dominate.
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