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 been dealt a mortal blow. The other Yoruba city-states broke free of Oyo dominance, and subsequently became embroiled in a series of internecine conflicts that soon metamorphosed into a full scale civil war. These events weakened the southern Yorubas in their resistance to British colonial and military invasions. In 1960, greater Yorubaland was subsumed into the Federal Republic of Nigeria. The historical records of the Yoruba, which became more accessible in the nineteenth century with the more permanent arrival of the Europeans, tell of heavy Jihad raids by the mounted Fulani warriors of the north as well as of endemic