Rwandan genocide was very much fueled by Belgian racial policies.
My point isn't that Africa would be a utopia if the European powers hadn't carved it up like a toddler with a birthday cake, my point is only that the borders as formed in most of Subsaharan Africa are completely arbitrary divisions which rely more on conflicting colonial interests than realities of the people on the ground.
Take a look at Nigeria if you want an example of how conflicting ethnic groups artificially forced together by an attempt of colonial powers to maintain some measure of control turns out. There's a reason most countries in Europe were either ethnically dominated empires, or ethnically homogenous nation-states - and likewise, there is a reason why European imperialists put great effort into dividing subject peoples abroad.
The ability to construct and sustain a state, or any community, is based on shared values and cultural memes.