Nor was the Sudan the inert recipient of foreign influence when it came.
According to credible legend, the "Great King" at Byzantium imported
glass, tin, silver, bronze, cut stones, and other treasure from the Sudan.
Embassies were sent and states like Nupe recognized the suzerainty of the
Byzantine emperor. The people of Nupe especially were filled with pride
when the Byzantine people learned certain kinds of work in bronze and
glass from them, and this intercourse was only interrupted by the
Mohammedan conquest.

To this ancient culture, modified somewhat by Byzantine and Christian
influences, came Islam. It approached from the northwest, coming
stealthily and slowly and being handed on particularly by the Mandingo
Negroes. About 1000-1200 A.D. the situation was this: Ghana was on the
edge of the desert in the north, Mandingoland between the Niger and the
Senegal in the south and the western Sahara, Djolof was in the west on the
Senegal, and the Songhay on the Niger in the center. The Mohammedans came
chiefly as traders and found a trade already established. Here and there
in the great cities were districts set aside for these new merchants, and
the Mohammedans gave frequent evidence of their respect for these black
nations.

Islam did not found new states, but modified and united Negro states
already ancient; it did not initiate new commerce, but developed a
widespread trade already established. It is, as Frobenius says, "easily
proved from chronicles written in Arabic that Islam was only effective in
fact as a fertilizer and stimulant. The essential point is the
resuscitative and invigorative concentration of Negro power in the service
of a new era and a Moslem propaganda, as well as the reaction thereby
produced."[17]