A desire for glory and profit from trade, missionary zeal, and considerations of global strategy brought Portuguese navigators to the West African coast in the late fifteenth century. Locked in a seemingly interminable crusading war with Muslim Morocco, the Portuguese conceived of a plan whereby maritime expansion might bypass the Islamic world and open new markets that would result in commercial gain. They hoped to tap the fabled Saharan gold trade, establish a sea route around Africa to India, and link up with the mysterious Christian kingdom of Prester John. The Portuguese achieved all these goals. They obtained access to the gold trade by trading along the Gulf of Guinea, establishing a base at Elmina ("the mine") on the Gold Coast (Ghana), and they made their way into the Indian Ocean, militarily securing a monopoly of the spice trade. Even the Christian kingdom turned out to be real; it was Ethiopia, although Portuguese adventures there turned sour very quickly. Portugal's lasting legacy for Nigeria, however, was its initiation of the transatlantic slave trade.

By 1471 Portuguese ships had reconnoitered the West African coast south as far as the Niger Delta, although they did not know that it was the delta, and in 1481 emissaries from the king of Portugal visited the court of the oba of Benin. For a time, Portugal and Benin maintained close relations. Portuguese soldiers aided Benin in its wars; Portuguese even came to be spoken at the oba's court. Gwatto, the port of Benin, became the depot to handle the peppers, ivory, and increasing numbers of slaves offered by the oba in exchange for coral beads; textile imports from India; European-manufactured articles, including tools and weapons; and manillas (brass and bronze bracelets that were used as currency and also were melted down for objets d'art). Portugal also may have been the first European power to import cowrie shells, which were the currency of the far interior.

Benin profited from its close ties with the Portuguese and exploited the firearms bought from them to tighten its hold on the lower Niger area. Two factors checked the spread of Portuguese influence and the continued expansion of Benin, however. First, Portugal stopped buying pepper because of the availability of other spices in the Indian Ocean region. Second, Benin placed an embargo on the export of slaves, thereby isolating itself from the growth of what was to become the major export from the Nigerian coast for 300 years. Benin continued to capture slaves and to employ them in its domestic economy, but the Edo state remained unique among Nigerian polities in refusing to participate in the transatlantic trade. In the long run, Benin remained relatively isolated from the major changes along the Nigerian coast.

The Portuguese initially bought slaves for resale on the Gold Coast, where slaves were traded for gold. For this reason, the southwestern coast of Nigeria and neighboring parts of the present-day Republic of Benin (not to be confused with the kingdom of Benin) became known as the "slave coast." When the African coast began to supply slaves to the Americas in the last third of the sixteenth century, the Portuguese continued to look to the Bight of Benin as one of its sources of supply. By then they were concentrating activities on the Angolan coast, which supplied roughly 40 percent of all slaves shipped to the Americas throughout the duration of the transatlantic trade, but they always maintained a presence on the Nigerian coast.

The Portuguese monopoly on West African trade was broken at the end of the sixteenth century, when Portugal's influence was challenged by the rising naval power of the Netherlands. The Dutch took over Portuguese trading stations on the coast that were the source of slaves for the Americas. French and English competition later undermined the Dutch position. Although slave ports from Lagos to Calabar would see the flags of many other European maritime countries (including Denmark, Sweden, and Brandenburg) and the North American colonies, Britain became the dominant slaving power in the eighteenth century. Its ships handled two-fifths of the transatlantic traffic during the century. The Portuguese and French were responsible for another two-fifths.

Nigeria kept its important position in the slave trade throughout the great expansion of the transatlantic trade after the middle of the seventeenth century. Slightly more slaves came from the Nigerian coast than from Angola in the eighteenth century, while in the nineteenth century perhaps 30 percent of all slaves sent across the Atlantic came from Nigeria. Over the period of the whole trade, more than 3.5 million slaves were shipped from Nigeria to the Americas. Most of these slaves were Igbo and Yoruba, with significant concentrations of Hausa, Ibibio, and other ethnic groups. In the eighteenth century, two polities--Oyo and the Aro confederacy--were responsible for most of the slaves exported from Nigeria. The Aro confederacy continued to export slaves through the 1830s, but most slaves in the nineteenth century were a product of the Yoruba civil wars that followed the collapse of Oyo in the 1820s.

The expansion of Oyo after the middle of the sixteenth century was closely associated with the growth of slave exports across the Atlantic. Oyo's cavalry pushed southward along a natural break in the forests (known as the Benin Gap, i.e., the opening in the forest where the savanna stretched to the Bight of Benin), and thereby gained access to the coastal ports.

Oyo experienced a series of power struggles and constitutional crises in the eighteenth century that directly related to its success as a major slave exporter. The powerful Oyo Mesi, the council of warlords that checked the king, forced a number of kings to commit suicide. In 1754 the head of the Oyo Mesi, basorun Gaha, seized power, retaining a series of kings as puppets. The rule of this military oligarchy was overcome in 1789, when King Abiodun successfully staged a countercoup and forced the suicide of Gaha. Abiodun and his successors maintained the supremacy of the monarchy until the second decade of the nineteenth century, primarily because of the reliance of the king on a cavalry force that was independent of the Oyo Mesi. This force was recruited largely from Muslim slaves, especially Hausa, from farther north.

The other major slave-exporting state was a loose confederation under the leadership of the Aro, an Igbo clan of mixed Igbo and Ibibio origins, whose home was on the escarpment between the central Igbo districts and the Cross River. Beginning in the late seventeenth century, the Aro built a complex network of alliances and treaties with many of the Igbo clans. They served as arbiters in villages throughout Igboland, and their famous oracle at Arochukwu, located in a thickly wooded gorge, was widely regarded as a court of appeal for many kinds of disputes. By custom the Aro were sacrosanct, allowing them to travel anywhere with their goods without fear of attack. Alliances with certain Igbo clans who acted as mercenaries for the Aro guaranteed their safety. As oracle priests, they also received slaves in payment of fines or dedicated to the gods by their masters as scapegoats for their own transgressions. These slaves thereby became the property of the Aro priests, who were at liberty to sell them.

Besides their religious influence, the Aro established their ascendancy through a combination of commercial acumen and diplomatic skill. Their commercial empire was based on a set of twenty-four-day fairs and periodic markets that dotted the interior. Resident Aro dominated these markets and collected slaves for export. They had a virtual monopoly of the slave trade after the collapse of Oyo in the 1820s. Villages suspected of violating treaties with the Aro were subject to devastating raids that not only produced slaves for export but also maintained Aro influence. The Aro had treaties with the coastal ports from which slaves were exported, especially Calabar, Bonny, and Elem Kalabari. The people of Calabar were Efik, a subsection of Ibibio, while Bonny and Elem Kalabari were Ijaw towns.

The Ijaw, who occupied the tidal area in proximity to the Igbo, had wrested a frugal living from the sale of dried fish and sea salt to the inland communities for centuries before the rise of the slave trade. Traditionally, they had lived in federated groups of villages with the head of the ranking village presiding over general assemblies attended by all the males. During the heyday of the slave trade in the eighteenth century, the major Ijaw villages grew into cities of 5,000 to 10,000 inhabitants ruled by local strongmen allied with the Aro. Their economies were based on the facilities they offered to slave traders. They were entrepreneurial communities, receiving slaves from the Aro for resale to European agents. Personal wealth rather than status within a lineage group was the basis for political power and social status. Government typically was conducted by councils composed of leading merchants and headed by an amanyanabo (chief executive), an office that in time became hereditary.

By the end of the eighteenth century, the area that was to become Nigeria was far from a unified country. Furthermore, the orientation of the north and the south was entirely different. The savanna states of Hausaland and Borno had experienced a difficult century of political insecurity and ecological disaster but otherwise continued in a centuries-long tradition of slow political and economic change that was similar to other parts of the savanna. The southern areas near the coast, by contrast, had been swept up in the transatlantic slave trade. Political and economic change had been rapid and dramatic. By 1800 Oyo governed much of southwestern Nigeria and neighboring parts of the modern Republic of Benin, while the Aro had consolidated southeastern Nigeria into a confederation that dominated that region. The Oyo and the Aro confederations were major trading partners of the slave traders from Europe and North America.

Data as of June 1991