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 orders from Oyo were strictly followed, and access to local markets was provided to Oyo merchants. The Oyo often demanded tribute in slaves. The tributary sometimes made war on other peoples to capture slaves for this. Oyo punished disobedience by wholesale slaughter of the community, as it accomplished in Allada in 1698. The Oyo Empire developed a highly sophisticated political structure to govern its territorial domains. Scholars have not determined how much of this structure existed prior to the Nupe invasion. Some of Oyo's institutions are clearly derivative of early accomplishments in Ife. After reemerging from exile in the early