Trans Saharan trade was the introduction of Islam to the West African society. In the eighth century Arab invaders overran all of coastal North Africa. They introduced the Berbers living there to the religion of Islam, and gradually the Berbers became Muslims. As traders, these Berbers carried Islam to sub-Saharan West Africa. From the eleventh century onward western Saharan Berbers, preached Islam to the rulers of Ghana, Mali, Songhai, and Kanem-Bornu.