WI no Tsetse fly?

[Straha]

If there was no such thing as a tsetse fly or the nagana pest disease
that it carries, horses and camels could move about freely in Africa
south of the Sahara, and long ago black Africa would have been
organized into Europe or Asia type kingdoms and empires, and Islam
would have swamped Africa long ago except perhaps for a few dense wet
jungle areas. Uncontrolled nomadic grazing would have overgrazed and
deforested much of East Africa into Middle East type desert long ago
and the land would be plagued with Bedouin-type mounted nomads
forever raiding. The tsetse fly is the defender of Africa

[NapoleonXIV]

Sub-saharan Africa was largely organized into Kingdoms that rivaled Europe as late as Medieval times. Great Zimbabwe, Benin, Dahomey, these are just a few (that I remember ), Most were destroyed by slavery, not the tsetse fly or the lack of horses/camels.

Overgrazing as the only cause of the desertification of the Fertile Crescent is, as I understand it, a matter of dispute. The destruction of irrigation works going back to far antiquity in Iraq by the Mongols is one factor in that area that's as little known as it is considered. Isn't overgrazing more of a modern phenomena?