Like him or not, he's compiled a lot of good information into this video.
Not directly related to what you're asking, but this is interesting to me:
"They" whichever power that brings it up within Africa - have plans where they dream of diverting part of the Congo River and part of the Niger River to Lake Chad. The rolling theory is that Lake Chad, and Lake Ahnet's (Maghreb Sea) sheer size created much of the precipitation on the continent during the Halocene Period (Lake Fezzon, and Agadez Sea to a much lesser extent, Im sure). I havent heard any feasible way to bring back lake Ahnet, but recreating the original size of Lake Chad would change the surrounding countries by leaps and bounds. Not only bringing vegetation back to those regions, but everything that comes along with vacant land and water. Not to forget, that having a water way connected to the congo means that interior nations like Chad could theoretically have container ships for trade/commerce.
Lake Chad was fed by these rivers in ancient times - diverting the water back doesnt seem far fetched in countries that arent fucking retarded. But of course this is Africa, and the people there would rather cut their fucking nose off rather than prosper.
The armies stopped rather early into Africa. But from what I understand, Romans mapped just about all of it.