A contemporary empire of Ghana, but less extensive, the kingdom of Tekrur was its vassal. Ghana and Tekrur were the only organized populations before Islamization. The territory of Tekrur approximates that of the current Fouta Toro. Its existence in the 9th century is attested by Arabic manuscripts. The formation of the state may have taken place as an influx of Fulani from the east settled in the Senegal valley. John Donnelly Fage suggests that Takrur was formed through the interaction of Berbers from the Sahara and "Negro agricultural peoples" who were "essentially Serer" although its kings after 1000 CE might have been Soninke (northern Mande). The name, borrowed from Arabic writings, may be linked to that of the ethnicity Toucouleur. Trade with the Arabs was prevalent. The Kingdom imported wool, copper and pearls and exported gold and slaves. Indeed, the growth of a vast empire by Arab-Muslim Jihads is not devoid of economic and political issues and brought in its wake the first real growth of the slave trade. This trade called the trans-Saharan slave trade provided North Africa and Saharan Africa with slave labor. The Tekrur were among the first converts to Islam, certainly before 1040.