What were the effects of Islam on the different culture of ancient African empires ?

I'm sure you'll find some ideas here:

http://www.bing.com/search?q=islamic+impact+in+africa&form=EDGNTC&qs=PF&cvid=112b500c1c0d423abd0cb64c3c8491b0&pq=islamic%20impact%20in%20africa