History of Africa usually governed by an "oba" and an "iwarefa", a council of chiefs who advised the "oba." by the 18th century, the Yoruba city-states formed a loose confederation, with the "Oni" of Ife as the head and Ife as the capital. As time went on, the individual city-states became more powerful with their "obas" assuming more powerful spiritual positions and diluting the authority of the "Oni" of Ife. Rivalry became intense among the city-states. The Oyo Empire rose in the 16th century. The Oyo state had been conquered in 1550 by the kingdom of Nupe, which was in possession of cavalry,
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