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
Nupe people Nupe people The Nupe, traditionally called the Tapa by the neighbouring Yoruba, are an ethnic group located primarily in the Middle Belt and northern Nigeria, and are the dominant group in Niger State, an important minority in Kwara State and present in Kogi State as well. The Nupe trace their origin to Tsoede who fled the court of Idah and established a loose confederation of towns along the Niger in the 15th century. The proximity of Nupe to the Yoruba Igbomina people in the south and to the Yoruba Oyo people in the southwest led to cross-fertilization of cultural influences