I'm completely lost with this, so any book recommendations or links would be useful, especially looking at the interactions between the different states? Anything at all really though, even historical fiction!
Jean-Pierre Chretien's The Great Lakes of Africa, which I'm currently reading, is a survey of 2000 years of interlacustrine history. (The bibliography could be particularly helpful.) Other works which could be helpful (but I haven't yet read) are: David Schoenbrun, A Green Place, A Good Place; David Newbury's various works; and possibly Jan Vansina's Antecedents to Modern Rwanda. Hope this helps!
look at the askhistorians booklist. The UNESCO histories of Africa (on the list) are free and cover this period. however this period is split up across two of their volumes and the research is a bit out of date so it's missing post 1999 advancements.