History of the Yoruba people military capital of Ilorin, and then sacked and destroyed Ọyọ-Ile, the royal seat of the Ọyọ Empire. Following this, Ọyọ-Ile was abandoned, and the Ọyọ retreated south to the present city of Oyo (formerly known as "Ago d'Oyo", or "Oyo Atiba") in a forested region where the cavalry of the Sokoto Caliphate was less effective. Further attempts by the Sokoto Caliphate to expand southwards were checked by the Yoruba who had rallied in defence under the military leadership of the ascendant Ibadan clan, which rose from the old Oyo Empire, and of the Ijebu city-states. However, the Oyo hegemony had
Oyo Empire within and outside of Yorubaland. It was divided into four layers defined by relation to the core of the empire. These layers were Metropolitan Oyo, southern Yorubaland, the Egbado Corridor and Ajaland. Metropolitan Oyo corresponded, more or less, to the Oyo state prior to the Nupe invasion. This was the hub of the empire, where the Yoruba spoke the Oyo dialect. Metropolitan Oyo was divided into six provinces, with three on the west side of the Ogun River and three to the river's east. Each province was supervised by a governor appointed directly by the Alaafin of Oyo. The second