Dyula (Wangara) were Mandinka tradesman who dominated trade during the Mali Empire. They were based in Jenne. They connected the forest trade networks to the western sahelian trade networks to North Africa. The Dyula established contacts with the forest zones transporting kola nuts, gold from the sahel, in return for cloth, cowries from North Africa controlled by the Tuaregs. The dyula was initially organized into independent companies, but were unified under the Dyula-Mansa or Shehu-Wangara, as referred to by the Hausa. For centuries, men carried the items of trade, exchanged ideas, and influenced one another.
Davidson, Basil, Buah, F. K. ,and Ajayi, J.F. Ade(1966). A History of West Africa. Doubleday:New York, pp. 71-72. Library of Congress Card #66-24317