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 and armament. All infantry in the region carried shields, swords and lances of one type or another. Shields were four feet tall and two feet wide and made of elephant or ox hide. A heavy sword was the main armament for close combat. The Yoruba and their neighbors used triple barbed javelins which could be thrown accurately from about 30 paces. The Oyo Empire, like many empires before it, used both local and tributary forces to expand its domains. The structure of the Oyo military prior to its imperial period was simple and closer aligned to the central government in