Tell that to these guys.
Transformations in Slavery: a history of slavery in Africa - Page 177
Or better yet, tell the Christians in Ethiopia, how their religion made them weak such that they are the only country in Africa that was never successfully colonized for any long period of time. Of course they did continue to practice slavery like other parts of Africa until they banned it as a condition of joining the League of Nations.
Ethiopia a Country Study - Page 56