The problem is that this mostly happened prior to written history in the region. The primary evidence for the Bantu expansion is linguistic relationships, and I suppose the absence of Khoi-San peoples today where cave paintings suggest they used to be in the past, but there is little evidence to determine whether this was a process of military conquest, peaceful subjugation, or even peaceful amalgamation of the peoples. The presence of distinctively Khoi-San clicks in both isiZulu and isiXhosa (absent in more northern Bantu languages) implies to me that the process probably leaned more towards the latter. But if someone can come up with reliable sources talking about actual historical evidence of battles that took place between Bantu peoples and Khoi-San peoples -