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 During the reign of Onigbogi, Oyo suffered military defeats at the hands of the Nupe led by Tsoede. Sometime around 1535, the Nupe occupied Oyo and forced its ruling dynasty to take refuge in the kingdom of Borgu. The Nupe sacked the capital, destroying Oyo as a regional power until the early 17th century. The Yoruba of Oyo went through an interregnum of 80 years as an exiled dynasty after its defeat by the Nupe. They re-established Oyo as more centralized and expansive than ever. The people created a government that established its power over a vast empire. During the