Oyo Empire metropolitan Oyo. This may have been fine in the 15th century when Oyo controlled only its heartland. But to make and maintain farther conquest, the structure underwent several changes. Oyo maintained a semi-standing army of specialist cavalry soldiers called the "Eso", the "Esho" or, formally, the Eso of Ikoyi. These were 70 junior war chiefs who were nominated by the Oyo Mesi and confirmed by the Alaafin of Oyo. The Eso were appointed for their military skill without regard to heritage and were led by the Are-Ona-Kakanfo. After Oyo's return from exile, the post of Are-Ona-Kakanfo was established as the
Yoruba people in the Atlantic slave trade Yoruba people in the Atlantic slave trade The Yoruba people, among the most heavily targeted, contributed significant cultural and economic influence upon the Atlantic slave trade during its run from approximately 1400 until 1900 CE. From 1400 onward, the Oyo Empire's imperial success made the Yoruba language a "lingua franca" almost to the shores of the Volta. Toward the end of the 18th century, the Oyo army was neglected as there was less need to conquer. Instead, Oyo directed more effort towards trading and acted as middlemen for both the Trans-Saharan and Trans-Atlantic slave trade. Europeans bringing salt arrived in