Abdul Hadi Pasha
Banned
East Africa is the key. Western European agricultural practices can be applied to the East African region in a way that they cannot in most of the rest of Africa, (including most of OTL South Africa). In OTL it never got that huge a level of settlement because it was too difficult to get to.
This is not true. One of the reasons why slavery in East Africa was so hard to eradicate is that sleeping sickness makes use of animal power impossible, so transport of goods had to be by human (slave) porter. The only areas suitable for European settlement and agriculture are limited to a couple of upland plateaus, which can't support too much population.
Also, by the time our technology and medical knowledge had advanced enough to make large-scale settlement possible, we had abandoned genocide as a legitimate way of freeing up territory - which would be necessary to accomplish your goal.