No two historical factors have been more deeply implicated in contemporary struggles between Nigeria’s diverse ethnic and religious groups than British colonialism and the transatlantic slave trade. The slave trade triggered unprecedented internal competition as groups defined themselves in contradistinction to others who could be enslaved. Additionally, slavery fostered greater contact with European merchants and stimulated European mercantilism and economic interest along the southern coast, thus laying the groundwork for colonialism and the economic changes it would bring.
Slavery, albeit in a much different form, was practiced in Africa independent of the transatlantic trade, which lasted from the late 15th to the 19th century. Slavery was permissible under Islamic law, although the enslavement of fellow Muslims was not and freeing slaves was considered a highly praiseworthy act. In the royal households of the Sokoto Caliphate, established in 1804, slaves were able to acquire prestige and even positions of military and administrative power by virtue of their close relationships and kinship ties with Sokoto leaders, similar to slaves in the Ottoman Empire, and in some cities in Northern Nigeria more than half of the population could have been considered slaves.3 Domestic slavery was prevalent in Yorubaland from at least the 15th century, one form of which was iwofa, where an adult or child was pawned to settle a debt and then freed afterwards. Thus, there were various types of indenture and slavery that differed from the system of chattel slavery developed in North America and the Caribbean.
Compared to the domestic forms of slavery outlined above, the magnitude of the transatlantic slave trade was far more destructive because through that vehicle West Africa’s power structures, economic relationships, and cultural patterns were radically reordered. European merchants hired local brokers, particularly among the Ayo, Oyo, and Hausa, to provide captive Africans, which triggered predatory internal struggles between groups and internecine warfare within groups to produce captives. The long-standing trans‐Saharan trade route became a raiding station, thereby disrupting centuries-old trade patterns. Also, slavery encouraged militarization and stratification, leading to the rise of warlords.
By the time the British outlawed slavery in 1807, northern Nigeria was deeply militarized and stratified. Lagos and other coastal cities in the southern Delta region had risen as important economic hubs where African merchants had longstanding European contact, setting the stage for polarization in the coming years. Throughout Nigeria, traditional leadership structures had been shuffled and even dismantled, leading to vulnerabilities and violence that left the country ripe for colonization.
 Humphrey J. Fisher, Slavery in the History of Muslim Black Africa (New York: New York University Press, 2001). Sean Stilwell, “The Development of ‘Mamluk’ Slavery in the Sokoto Caliphate,” in Slavery on the Frontiers of Islam, ed. Paul E. Lovejoy, (Princeton: Marcus Wiener Press, 2004), pp. 87–110.
 Toyin Falola and Akanmu Adebayo, Culture, Politics, and Money Among the Yoruba (New Brunswick: Transaction Publishers, 2000).
 Toyin Falola and Saheed Aderinto, Nigeria, Nationalism, and Writing History (Rochester: University of Rochester Press, 2010).