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
Oyo Empire Dahomey in the modern Republic of Benin to the west. The origins of the Oyo Empire lie with Oranyan (also known as Oranmiyan), the last prince of the Yoruba Kingdom of Ile-Ife (Ife). Oranyan made an agreement with his brother to launch a punitive raid on their northern neighbors for insulting their father Oduduwa, the first Ooni of Ife. On the way to the battle, the brothers quarreled and the army split up. Oranyan's force was too small to make a successful attack, so he wandered the southern shore until reaching Bussa. There the local chief entertained him and provided