I'm afraid my knowledge of modern Africa is quite basic so you'll have to forgive my generalities.
And yet the consequences of colonialism and the conditions that brought it about were not.
You'd have to be pretty stupid to believe centuries of political destabilization, subordination, exploitation and destitute poverty could be done away with overnight, and you'd have to be pretty ignorant to assume after the 1960's the former-colonial powers didn't still have a vested interest in the continent.
Off the top of my head look at Patrice Lumumba. Somewhat progressive guy, anti-colonial, democratically elected; unfortunately a little too left and certainly a little too cosy with the Soviets so America backed a coup, overthrew him and installed Mobuto Sese Seko, one of the most corrupt leaders in Africa. Not that that matters though because he was their guy.