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
History of the Yoruba people to earth. They became popular with their trading with the Portuguese, which gave them guns for their trade. The Yoruba people were invaded by the Fulani which pushed the people to the South. In the late 1800's, they formed a treaty with the Fulani people and were colonized with the British in 1901. The people who lived in Yorubaland, at least by the seventh century BC, were not initially known as the Yoruba, although they shared a common ethnicity and language group. The historical Yoruba develop "in situ", out of earlier (Mesolithic) Volta-Niger populations, by the 1st millennium BC. Archaeologically,