Did I miss this? I remember the thread but not this paragraph.
One very serious suggestion is the lack of water transport. Before railroads,
the only way to move heavy objects was by water. Almost all ancient advanced
civilizations were based around year-round navigable rivers and ocean ports.
The few that weren't (like the Central Asiatics) were generally based around
conquering the rest or trading their luxury good. In Sub-Saharan Africa,
virtually all the rivers are highly seasonal and unnavigable most of the
year, and there are virtually no harbors. Most of the better rivers, like
the Congo, serve jungles which are not very good habitat for people.
Send me a message if you want me to look up the references.