Not all problems in Africa are solely related to European imperialism. On the part of slavery, we should also take in consideration that slavery already existed on quite a large scale in Africa before the arrival of Europeans. 'Slaves were employed as domestic servants, they acted as carriers, they maintained oases and cut rock salt from the desert, they laboured to build towns, construct roads and clear paths, they were drafted as front line troops, and they were common in all types of agricultural work' (Hopkins, 1973). The first slaves to be deported from Africa by Europeans were mostly "traded" by local African leaders, with the slaves being predominantely members of hostile nations. On the other hand, we should also take in consideration that it were the Europeans who really triggered it off (the slavetrade), which lead to the deportation of more than 11 million black slaves from Africa to the Americas.
But to come back on the original subject: the conflict described in Congo is often called "the lost World War", or "the World War of Africa"; in this conflict - which started in 1998, and officially ended in 2003, though fighting still continues in some parts of the country (Congo), as well as in neighbouring countries like Rwanda - an astonishing 3,5 million people have died (in Eastern Congo alone that is, I don't have all figures). But I can assure you, if you go ask people about whether they have heard about this war, few - very few - will say yes.