Mali is the land of Timbuktu. In pre-colonial days, I believe it was the richest of all of Africa's kingdoms, sub-Saharan or otherwise. It is a shame, in many ways, they listened to us on agricultural methods, as they clearly knew what they were doing prior to our arrival.
Well actually did its finest day end a little bit earlier. They lost most of thier power during the 1600:th century. But you're correct that it was a very rich empire, mostly due to trade IIRC.