Fulbe merchants accepted salt and horses from North Africa in exchange for slaves for sale in the Muslim empires to the north.
From the en.wikipedia.org
More examples
Fulani: a member of a pastoral and nomadic people of western Africa; they are traditionally cattle herders of Muslim faith
Fula or Fulani or Fulbe (the latter being an Anglicisation of the word in their language, Fule) are an ethnic group of people spread over many countries, predominantly in West Africa, but found also in Central Africa and Sudanese North Africa. ...