mostly their movement was a natural evolution,steady movement thru millenia,ofc there could be skirmishes here and there but in that lush environment i doubt anyone cared who was nxt door ,it was enough to feed all. and the surrounding communities were very much identical in terms of looks.What I'm more interested in is the displacement of the Nilosaharans and South Cushites that predominately occupied S.E Africa before the slash-and-burn Bantus flocked in.
I am not being politically correct but they came from the West and displaced various foraging peoples in part from crop cultivation and by being well-armed.
Never would they have been successful in the Horn. They already had weapons and were more advanced.
they couldnt cross the desert barrier in the horn,it was alien to thm,kind from riches to rags.