[nroets]

The Khoisan have occupied much of Africa for much of human history. [1] I don't know exactly how the Bantus displaced the people that they came across, but I suspect some form of foul play.

1: http://www.nature.com/articles/ncomms6692

[buyx]

How would you explain the integration of Khoisan click consonants in Bantu languages if foul play was involved?

[mveety]

Things like that come from "cultural contact" which can be peaceful or violent.