I am reading The Great African War by Filip Reyntjens. It is about the war(s) in and around the Congo and Rwanda in the 1990’s. He writes:
the seeds of instability were sown in the beginning of the 1960s: the massive exile of the Rwandan Tutsi, who fled to neighbouring countries during and after the revolution of 1959-1961, and the virtual exclusion of Tutsi from public life in Rwanda, the radicalisation of Burundian Tutsi who monopolised power and wealth and the insecure status of Kinyarwanda-speakers in the Kivu provinces – all these factors were to merge with others to create the conditions for war. The acute destabilisation of the region started on 1 October 1990 when the Rwanda Patriotic Front (RPF) attacked Rwanda from Uganda with Ugandan support.