One of the most stable countries in Africa is Botswana. Why ? Because the population is predominantly from one tribe, The Tswana. Most other countries have competing tribes, which causes conflict. The ultimate conflict being the genocide in Rwanda. If the dividing up of the continent by European colonists had not happened and countries had evolved on tribal boundaries it may be a more peaceful place.
In some cases when the trial territory was big, the colonists even created a tribal difference, or the same twice being inside 2 different empires now are enemies etc.