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 There are three major dialect areas: Northwest, Central, and Southeast. As the North-West Yoruba dialects show more linguistic innovation, combined with the fact that Southeast and Central Yoruba areas generally have older settlements, suggests a later date of immigration for Northwest Yoruba. The area where North-West Yoruba (NWY) is spoken corresponds to the historical Oyo Empire. South-East Yoruba (SEY) was probably associated with the expansion of the Benin Empire after c. 1450. Central Yoruba forms a transitional area in that the lexicon has much in common with NWY, whereas it shares many ethnographical features with SEY. Literary Yoruba, the standard