Slavery existed in Africa long before they ever heard the word 'christianity'. Just as it had in asia. What I don't think you have comprehended is that slavery has existed, and has been 'accepted' since the dawn of mankind.
The Islamic Ascension in the North African region saw the rise of WHITE slaves from slavic regions, who were their favored type of slave.
So please, if you really want to see who promotes and pushes 'slavery', you need look no further than what muslims are doing to people all over the world TODAY.