Military history and/or war are not really my areas, but there are plenty of texts (especially articles) on war in pre-19th century Africa. Richard Reid is a big scholar in this area. I recommend his War in Precolonial East Africa (Ohio U Press 2007) and also the first three chapters or so of Warfare in African History (Cambridge 2012). I have not read Lamphear's African Military History (Ashgate 2007) nor Timothy Stapelton's Military History of Africa (Praeger 2013), of which Vol. 1 covers history before 1870.

What you will note, I'm sure, is that we certainly know enough for there to be a literature on the topic! I do think a lot of "armed conflict" also gets discussed outside of the "military history" title because low-level conflict was often engaged with religious and political change, economic transformations, etc.

Do you mean indigenous pre-Bantu civilizations? Or before widespread European colonialism? Because those two are very different.