Robin Law's The Ọyọ Empire, c.1600-c.1836: a West African imperialism in the era of the Atlantic slave trade was one of those important studies of a major West African polity that we found difficult to read a year ago. We believed it was relying too heavily on fragmentary traditions and hearsay that entered into the contemporary European sources to be sufficiently accurate. However, since it was published in the 1970s and of course relied heavily on local oral traditions in addition to classic studies by Yoruba authors like Johnson, we decided to revisit Law's book. As he himself admitted, his study relied on limited sources and some of its conclusions will hopefully be advanced or rebutted by subsequent scholarship. Nonetheless, as one would expect from a meticulous like Law who has written extensively on the Slave Coast, his study of the Oyo Empire during the same era endeavors to contextualize Oyo's expansion in the era of the Trans-Atlantic Slave Trade.
Oyo, as major supplier of captives to the ports of the Slave Coast, was, however, a hinterland kingdom based on a cavalry force. This cavalry, supplied from the north, meant Oyo was deeply connected to Nupe, Bariba, and even Hausaland and Borno for horses, equipment, and goods acquired through trans-Saharan trade. Thus, Oyo provides an interesting example of an Atlantic trading state (which for a time commanded tribute from Porto Novo, Badagry, Allada and Dahomey) which also had close ties to the savanna states to the north. Indeed, the mention of "Yoruba" slaves by Timbuktu scholar Ahmad Baba and the trade in horses and slaves between Kano and the Nupe must have brought the Oyo Yoruba into contact with Muslim Sudanic West African traders by the 16th century. After a period of Bariba and Nupe rule, a resurgent Oyo was able, by the 1600s, able to expand and use its own cavalry to assert itself effectively in savanna territories around Oyo (and the southwest). Even some hilly areas or regions with politically fragmented Yoruba fell under Oyo rule, through a combination of Oyo colonists and military force. Gradually, Oyo was able to profit from both the Atlantic trade via the coast as well as the northern trade routes that linked it to the Sudanic regions.
Instead of providing captives to the north in exchange for horses, like in its earlier period of growth, Oyo was able to trade cowries and European goods for horses from northern suppliers. Indeed, by the late 18th century, with access to the coast through ports like Porto Novo, Oyo was likely a major supplier of Hausa and northern slaves to the Atlantic trade. Oyo's own textile industry and far-ranging traders also continued to prosper, seeming to avoid any negative internal impact of the slave trade (such as insecurity) until its later years of decline. Indeed, Oyo may have benefitted from a more monetized economy stimulated by trade, cowries, textiles, foodstuffs produced for traders (and captives) and redistributed imported European goods or silks, natron and leather goods from the north. Oyo, like Dahomey and Asante, appears to have been able to combine imperial expansion and Atlantic slave trade to become wealthier states. Unfortunately for Oyo, however, political centralization did not reach the level of Benin, Dahomey or Asante. The alafins of Oyo were never able to completely subdue the powerful Oyo Mesi and the Basorun, who controlled the capital's army. Instead, the alafins of Oyo had to rely on palace slaves and officials they appointed to oversee provinces, collect tribute, and command the provincial army to expand the state and increase their own power.
However, after Basorun Gaha seized power in the middle of the 18th century, Abiodun was only able to restore the alafin to effective authority through an alliance with the head of the provincial army. This, however, led to further problems with the coup d'etat against Awole in c.1796, when the head of the provincial army decided to rebel against Awole. This, followed by Afonja inciting a Muslim rebellion and further conflict between provincial leaders against an Alafin who could accumulate too much power, paved the way for Oyo's eventual collapse. Oyo, according to Law, was thus unable to attain a comparable degree of centralization to that of Benin, Dahomey and Asante. Whether or not it was really due to the reliance on cavalry for the military (the costs of maintenance for imported horses being too costly for kings alone to finance), Law appears to be correct in noting the lack of adequate centralization to ensure imperial stability. Consequently, after reaching perhaps its imperial and slave trading peak in the 1780s, Oyo declined afterwards as Afonja and the repercussions of Uthman dan Fodio's jihad destroyed Oyo.
What we find interesting about Oyo is in its role as an imperial middleman between the Sudanic states and the Atlantic. Horses from the north, captives and luxuries acquired through the trans-Saharan trade were sold in Oyo just as European products and cowries circulated north. Oyo, through its reliance on cavalry, may have lacked the degree of centralization of Borno (despite a similar "fief" system of allocating tribute rights) since it had to incur the costs of importing horses and maintenance. Oyo, nonetheless, appears to have faced limitations on its expansion as the forested southern Yorubaland territories were able to resist cavalry. Northern expansion was thwarted by the Nupe and Bariba states who possessed easier access to horses, even if Oyo did succeed in imposing tribute on southern Nupe and Bariba states. Even Oyo expansion to the southwest, for access to the coast through Dahomey and Porto Novo, was likewise limited by the rainy season that made it difficult to permanently retain control over the area. In conclusion, Oyo may have been more restricted than some of its northern, cavalry-based trading partners due to the geographic and climate factors in Lower Guinea. Perhaps these checks imposed on Oyo expansion contributed to the weakening of centralization? If, perhaps, an interior kingdom with access to horses had been able to permanently conquer and administer Dahomey and Porto Novo, unhindered access to Atlantic trade and ongoing northern economic exchange may have stimulated a more centralized Oyo with effective use of firearms?