The empire grew to become the largest Yoruba-speaking state through the organizational and administrative efforts of the Yoruba people, trade, as well as the military use of cavalry.

The legendary origins of the Oyo Empire lie with Oranyan (also known as Oranmiyan), the last prince of the Yoruba Kingdom of Ile-Ife (Ife).

According to oral traditions, Oranmiyan made an agreement with his brother to launch a punitive raid on their northern neighbors for insulting their father Oduduwa, the first Ooni of Ife.

[5] Oranmiyan's force was too small to make a successful attack, so he wandered the southern shore of the Niger River until reaching Bussa.

Not long after the war was won, Oranmiyan had a son, Ajuwon Ajaka, by Princess Torosi of the Tapa (Nupe); much later Arabambi was also born by the same woman.

[28] The Basorun was a key political office in the Oyo (often likened to the role of the Prime Minister and Chancellor of the Kingdom) during the 16th to 18th centuries, controlled by Ibariba families.

For instance, by custom, the Alaafin abstained from leaving the palace, except during the important festivals, which in practice curtailed his power.

Led by the Bashorun, acting as prime minister, and consisting of the Agbaakin, the Samu, the Alapini, the Laguna, the Akiniku, and the Ashipa, they represented the voice of the nation and had the chief responsibility of protecting the interests of the empire.

[34] The head of the council of Oyo Mesi, the Bashorun, consulted the Ifa oracle before the royal succession for approval from the gods.

Once given the calabash or the parrot's eggs, the Alaafin, his eldest son the Aremo, and his personal counselor within the Oyo Mesi, the Asamu,[34] all had to commit suicide to renew the government.

The Ogboni was a very powerful secret society composed of aristocratic freemen noted for their age, wisdom, and importance in religious and political affairs.

[35] Because its main geographic focus was north of the forest, Oyo enjoyed easier farming and thus a steady growth in population.

[15][38] Despite its drawbacks, Oyo managed to amass one hundred thousand cavalry horsemen, earning the fear of many kingdoms and empires across West Africa.

The Eso were led by the Aare-Ona-Kakanfo,[30] and were famous for living by a warrior code that was comparable to the Latin dictum infra dignitatem.

[44] Tributary leaders and provincial governors were responsible for collecting tribute and contributing troops under local generalship to the imperial army in times of emergency.

Elite residences in Oyo-Ile showcased a distinctive architectural style, highlighted by intricate sculptures that symbolized the status of the inhabitants.

Sculptors adorned houses and compounds with finely carved wooden posts and bas-relief doors, often depicting narratives of significant events, asserting power, and immortalizing the experiences of the residents.

The structure, perfectly square and approximately twenty yards on each side, featured polished, deep-red stained floors and walls.

For example, a temple in Ilaro was described as a large square building supported by round pillars, against which were set sculptures of men, some armed with sword and shield and others holding pistols.

Clapperton noted the remarkable skill of the artisans, stating that some of their sculptural creations rivaled those he had seen in Europe in terms of delicacy.

[24] It is known that at least some Muslim officials were kept in Metropolitan Oyo,[48] and men capable of writing and calculating in Arabic were reported by French traders in 1787.

In his quest for absolute power, Gaha conspired with the Oyo Mesi and probably to some extent the Ogboni to force four successive Alaafins to commit ritual suicide after they had been presented with the symbolic parrot's eggs.

Alaafin Abiodun during his reign had also conducted failed campaigns against Borgu in 1783[51] and Nupe in 1789,[52] losing the equivalent of 11 and 13 generals and their men respectively.

Afonja, being bound by an oath and also desirous not to fall under a curse from a previous Alaafin made to the effect that any Aare Ona Kakanfo who attacked Iwere-Ile (his paternal home) was to die miserably, refused to comply.

Shehu Alimi, a Fulani chief who was the leader of the growing Muslim population in Oyo, also rose to power at this time.

[55] By the time Captain Hugh Clapperton visited Oyo-Ile in 1825 during the reign of Alaafin Majotu, the empire was already in a state of decline.

[55] Ilorin then besieged Offa and started raiding, burning and pillaging villages in Oyo, eventually destroying the capital Oyo-Ile in 1835.

[53] As Oyo tore itself apart via political intrigue, its vassals began taking advantage of the situation to press for independence.

The Egba, under the leadership of a war chief called Lishabi, massacred the Ilari stationed in their area and drove off an Oyo punitive force.

Oba Atiba sought to preserve what remained of Oyo by placing on Ibadan the duty of protecting the capital from the Ilorin in the north and northeast.