In the early 1660s, when the events described in Behn's Oroonoko (NAEL 8, 1.2183) are supposed to have taken place, England was not yet a major power in the slave trade. Portugal had been actively engaged in the traffic in African slaves for more than two centuries; Spain had built a lucrative sugar empire by importing slave labor to the New World; and as early as the 1560s, the English captain John Hawkins had plundered slaves from Africa and Latin America. But only in 1660, when Charles II helped found a new company, the Royal Adventurers into Africa, did England fully enter the trade. The first ships took slaves from the African Gold Coast (Guinea) to Surinam and Barbados, a flourishing sugar island in the Caribbean; by the early eighteenth century, the leading colony for sugar and slaves was Jamaica. The trade continued to grow. In 1713 Great Britain was awarded the contract (asiento) to import slaves to the Spanish Indies, and the South Sea Company, which bought the contract, excited frenzied speculation. This was a risky business, but the profits could be immense. Bristol, then Liverpool, developed into prosperous slave ports, trading manufactured goods to Africa for human cargo, which crossed the Atlantic on ships that returned to England with sugar and money. By the 1780s, when Britain shipped a third of a million slaves to the New World, the national economy depended on the trade.

The human cost was terrible. Though slavery in Africa had long been common, the deadly voyage — the Middle Passage — across the Atlantic made it something unfamiliar, brutal, unendurable. Torn from their homes, slaves were often packed into spaces too small to allow them to turn, with barely enough food and drink and air to keep them alive. It is estimated that 10 percent, on average, died on each crossing; on a bad voyage the figure might rise above 30 percent. Revolts and mutinies were common, though seldom successful (since the slaves had nowhere to go), and were ruthlessly punished. Nor did those slaves who survived the crossing feel fortunate for long. On the labor-intensive Caribbean sugar plantations, so many died that new shiploads were constantly needed (the situation was different in North America, where slaves lived on to reproduce and grow in numbers). Black people also lost their ties to the cultures in which they had been born. Mixed together from different regions of Africa, without a common language or background, they came to be identified merely by the color of their skin. It was convenient for owners of slaves to regard them as less than human.

The loss of humanity rebounded on Britain as well. The English had long regarded themselves as a people uniquely devoted to liberty, whose spirit was embodied in the rights of Magna Carta (1215). James Thomson spoke for patriotic pride in the chorus of "Rule, Britannia" (NAEL 8, 1.2840): "Rule, Britannia, rule the waves; / Britons never will be slaves." But British rule meant slavery for others. The deep contradictions of this position were reflected in the political philosophy of John Locke and the interpretations of law by William Blackstone. Some Britons avoided shame by arguing that slavery had uplifted negroes, since it had introduced them to Christianity and civilization; one African American poet, Phillis Wheatley, expressed her gratitude for this conversion. But many Britons were troubled. Humanitarian feelings grew in strength throughout the later eighteenth century. A famous, sentimental exchange of letters between the black writer Ignatius Sancho and Laurence Sterne, the author of Tristram Shandy, displays their mutual sympathy for the victims of the slave trade. Such cruelty was a libel on human nature.

By the 1780s a wave of abolitionist fervor swept through Great Britain, led by the Quakers and, in Parliament, by William Wilberforce (1759–1833). The Society for the Abolition of the Slave Trade, founded in 1787, inspired many abolitionist poets to join the campaign. A few years later the French Revolution, and the wars that followed, caused a conservative backlash in Britain. Boswell, who had earlier argued the case for slavery against Samuel Johnson (NAEL 8, 1.2849), wrote a poem advocating "No Abolition of Slavery" in 1791. But Wilberforce won in the end, and a bill abolishing the British slave trade became law in 1807. That did not, of course, put an end to illegal trade, let alone slavery itself. The conflict between boasts of liberty and the enslavement of human beings passed from Britain to America, where its consequences would be written in blood. Yet the eighteenth century, which witnessed the high tide of the slave trade, also gave rise to the ideals of freedom, equality, and human rights that led to its doom.