The Songhai Empire was one of the biggest empires that the African continent had on its soil. It was located from the Atlantic coast, where Senegal and Gambia are now, through the northern part of Western Africa, and parts of the western Sahel, having the Niger River running in the middle of the empire.
This empire was Muslim one. Since it managed to expand significantly over territories that were not Muslim, it managed to spread out the religion. The people that were incorporated in this empire were not always willing to accept the new religion, so often it was by force, but little by little the Songhai Empire managed to convert the majority of the population in its territory to the Islam. That strengthened the Islam in Africa, and it had a large region where it became dominant, which is also evident in the present day.