These empires in West Africa, away from the coast to the south were in existence around 16th century. Colonialists used the term 'Western Sudan'. Sudan means land of black people to differentiate from the fair skinned Arab and Meghreb people to the north. Songhay empire was the largest. they were thriving on inter-saharan trade carried out mostly Arabs. The chief item of trade was gold from 'Ghana' which was known as Gold coast, Ivory and precious stones. Islam was the religion which found a firm footing and staunch followers. Schools for islamic learning were founded under royal patronage. These were the centers of culture of West Sudan.
Slave trade carried on initially by Moors and then by Europeans had links to the empires, though trade was coast based. The African populations of the new world (Americas) owe their origin to these regions and times.