Perhaps the most influential consequence of the trans-Saharan trade was the introduction of Islam to West Africa. In the eighth century Arab invaders overran all of coastal North Africa. They introduced the Berbers living there to Islam (see “Reasons for the Spread of Islam” in Chapter 9), and gradually the Berbers became Muslims. As traders, these Berbers carried Islam to sub-Saharan West Africa. From the eleventh century onward militant Almoravids, a coalition of fundamentalist western Saharan Berbers, preached Islam to the rulers of Ghana, Mali, Songhai, and Kanem-Bornu. These rulers, admiring Muslim administrative techniques and wanting to protect their kingdoms from Muslim Berber attacks, converted to Islam. Some merchants also sought to preserve their elite mercantile status with the Berbers by adopting Islam. Muslims quickly became integral to West African government and society. Hence, from roughly 1000 to 1400, Islam in West Africa was a class-based religion with conversion inspired by political or economic motives. Rural people in the Sahel region and the savanna and forest peoples farther south, however, largely retained their traditional animism.

Conversion to Islam introduced West Africans to a rich and sophisticated culture. By the late eleventh century Muslims were guiding the ruler of Ghana in the operation of his administrative machinery. Because efficient government depends on keeping and preserving records, Islam’s arrival in West Africa marked the advent of written documents there. Arab Muslims also taught Ghana’s rulers how to manufacture bricks, and royal palaces and mosques began to be built of brick. African rulers corresponded with Arab and North African Muslim architects, theologians, and other intellectuals, who advised them on statecraft and religion. Islam accelerated the development of the West African empires of the ninth through fifteenth centuries.

After the Muslim conquest of Egypt in 642 (see “Islam’s Spread Beyond Arabia” in Chapter 9), Islam spread southward from Egypt up the Nile Valley and west to Darfur and Wadai. This Muslim penetration came not suddenly by military force but, as in the trans-Saharan trade routes in West Africa, gradually through commercial networks.

Muslim expansion from the Arabian peninsula across the Red Sea to the Horn of Africa, then southward along the coast of East Africa, represents a third direction of Islam’s growth in Africa. From ports on the Red Sea and the Gulf of Aden, maritime trade carried Islam to East Africa and the Indian Ocean. Muslims founded the port city of Mogadishu between the eighth and tenth centuries, today Somalia’s capital. In the twelfth century Mogadishu developed into a Muslim sultanate. Archaeological evidence, confirmed by Arabic sources, reveals a rapid Islamic expansion along Africa’s east coast in the thirteenth century as far south as Kilwa, where Ibn Battuta visited a center for Islamic law in 1331.