After the independence of many African countries (not all, for example, Ethiopia was never really colonized), the countries struggled both politically and economically - even more than before the independence.
A huge reason for that is that the countries were not formed along the ethnic lines, but instead they were divided by the Europeans among themselves, so when the independence was gained, there were many internal conflicts between the ethnicities and religions.
One example for this was the Rwandan Genocide - a result of the conflict between the Hutu and the Tutsi.