Oyo Empire culture in Oyo where victory was obligatory and defeat carried the duty of committing suicide. This do-or-die policy no doubt contributed to the military aggressiveness of Oyo's generals. The Oyo Empire was the only Yoruba state to adopt cavalry; it did so because most of its territory was in the northern savannah. The origin of the cavalry is disputed; however, the Nupe, Borgu and Hausa in neighboring territories also used cavalry and may have had the same historical source. Oyo was able to purchase horses from the north and maintain them in metropolitan Oyo because of partial freedom from the
Yoruba people in the African slave trade during the 18th century. The Yoruba often demanded slaves as a form of tribute of subject populations, who in turn sometimes made war on other peoples to capture the required slaves. Part of the slaves sold by the Oyo Empire entered the Atlantic slave trade. Most of the city states were controlled by Obas (or royal sovereigns with various individual titles) and councils made up of Oloyes, recognised leaders of royal, noble and, often, even common descent, who joined them in ruling over the kingdoms through a series of guilds and cults. Different states saw