The history of present-day Oyo State is closely connected to the rise of the Oyo Empire, one of the most powerful political systems in pre-colonial West Africa. The empire developed among the Yoruba and became a major regional power through its political organisation, cavalry, military strength and extensive trading relationships.
The Alaafin was the political and spiritual head of the empire, while powerful institutions such as the Oyo Mesi and the Are-Ona-Kakanfo played important roles in governance and warfare. The system created a balance between the authority of the Alaafin and powerful political institutions.
The empire expanded across large parts of present-day southwestern Nigeria and neighbouring territories. Its influence extended through military campaigns, trade, diplomacy and tributary relationships. Horses and cavalry played a particularly important role in Oyo's military strength because of the relatively open savanna north of the forest zone.