Who spread Islam to other parts of Africa?

Answer 1

Islam came to areas outside of North Africa in three different ways, depending on whether we are speaking about the Horn of Africa (Ethiopia, Eritrea, Djibouti, and Somalia), West Africa (Ghana and Mali), or the lower East African coast (Kenya, Tanzania, and Mozambique).

Horn of Africa
The Horn of Africa was primarily converted by military conquest. Muslim leaders in the Sudan pressed further south and conquered several regions close to Ethiopia. By the 9th century, the Adal Sultanate, an indigenous Islamic Kingdom founded by people converted in the wake of Sudanese conquests, was competing with Aksum (the Ethiopian Christian Kingdom) for power in the Horn of Africa. Alliances between indigenous Islamic Kingdoms and more powerful Islamic States, like the Ottoman Empire, led to increased military successes for local Islamic Kingdoms against Christian Ethiopia and increased conversions to Islam.

West Africa or Sahel Region
Initially, in the 800s, Islamic Berbers and Arabs along the northern coast of Africa traded with Sahelian African merchants, especially the large and powerful Ghana Empire. As Islam was a stronger and more codified religion than those practiced by the Ghanians, Islam spread quite quickly among the cognoscenti from those interactions, primarily because the Ghanian leaders were entranced by technologies brought by the Muslims like writing. By the mid-900s C.E. Islam had come to dominate the Ghana Empire and was beginning to dominate elsewhere in Sahel region. Successor Islamic States, like the Mali Empire and the Songhai Empire, further popularized Islam in the region, the former through economic prosperity and magnanimity and the latter through violent conquest and expansionism.

East African Coast
Initially, in the late 1000s and 1100s, Islamic merchants from Arabia had interactions with East African merchants, especially on the island of Zanzibar. These contacts resulted in willful and free religious conversions by many local East Africans to Islam. In the following centuries, when Islam was the dominant religion among the coastal peoples, indigenous Islamic States were established. Additionally, Omani authorities began to form quasi-colonies along the East African coast to facilitate trade. Both indigenous Islamic States and Omani occupation resulted in increased conversions to Islam.