What Was the Transatlantic Slave Trade?

The transatlantic slave trade was a triangular commercial system operating between Europe, West Africa and the Americas from the mid-fifteenth century to the nineteenth century. European ships — Portuguese, Spanish, Dutch, French and British — carried manufactured goods (textiles, metalwork, firearms, alcohol) to the West African coast, where these goods were exchanged for enslaved people. The enslaved people were then transported across the Atlantic in conditions of deliberate brutality — the crossing known as the Middle Passage — to be sold in the Americas and the Caribbean, where they were forced to labour on plantations producing sugar, tobacco, cotton, coffee and rice. The ships then returned to Europe laden with these plantation goods, completing the triangle.

At its peak, the trade involved hundreds of ships, thousands of merchants, and tens of thousands of enslaved Africans crossing the Atlantic every year. The total number of Africans transported across the Atlantic between 1501 and 1875 is estimated at approximately 12.5 million by the Trans-Atlantic Slave Trade Database maintained by Emory University. Of these, an estimated 1.8 million died during the Middle Passage. Britain alone transported approximately 3.1 million of the total.

This was not an accident or a marginal activity. It was an organised, state-backed, legally protected system of human exploitation that generated the wealth upon which much of modern Western prosperity was built.

Origins: Portugal and the Beginning of Atlantic Slavery

The transatlantic slave trade did not spring fully formed from the mind of a single nation. Its origins lie in Portuguese exploration of the West African coast in the mid-fifteenth century.

In 1441, the Portuguese captain Antão Gonçalves brought the first enslaved Africans to Portugal from the coast of modern Mauritania. In 1444, a public slave auction was held in Lagos in southern Portugal — the first organised sale of enslaved Africans on European soil. Over the following decades, the Portuguese established a systematic trade: forts and trading posts along the West African coast, diplomatic relations with African coastal kingdoms, and an organised commerce in enslaved people to supply labour for plantations in the Atlantic islands of Madeira, the Azores and São Tomé.

When the Portuguese established colonies in Brazil from 1500 onwards, and when the Spanish began colonising the Caribbean and South America following Columbus’s 1492 voyage, the demand for enslaved labour exploded. The indigenous populations of the Americas were devastated by European diseases and colonial violence; enslaved Africans were deemed more physically resilient and were already part of an established commercial network. The asiento — the contract granting exclusive rights to supply enslaved Africans to Spanish colonies — became one of the most lucrative prizes in European commercial politics.

Britain Enters the Trade: John Hawkins and the Elizabethan Slavers

England entered the slave trade as a systematic commercial enterprise in 1562, when John Hawkins — backed by a consortium of London merchants including the future Lord Mayor of London — made the first English slaving voyage. Hawkins sailed to Sierra Leone, where he seized approximately 300 Africans (partly by capturing a Portuguese slave ship, partly by raiding villages), and transported them to Hispaniola, where he sold them to Spanish colonists in defiance of the Spanish Crown’s asiento monopoly.

The voyage was profitable. Queen Elizabeth I was initially disturbed by reports of the means — kidnapping Africans, she reportedly remarked, was “detestable and would call down the Vengeance of Heaven” — but when Hawkins demonstrated the financial returns, she invested royal ships in his subsequent voyages. By his third voyage in 1567–68, Hawkins commanded a fleet of six ships including the royal vessels Jesus of Lübeck and Minion. Elizabeth’s moral reservations had not survived the profit motive.

Hawkins was not the only Elizabethan to see the commercial possibilities. Sir Francis Drake — who served under Hawkins on the disastrous 1567 voyage — was himself a slaver. The trade attracted the same class of adventurer-merchant who were simultaneously building England’s commercial empire in Asia and the Americas.

The Royal African Company: State-Backed Slavery

For most of the seventeenth century, England’s participation in the slave trade was organised through monopoly companies. The most significant was the Royal African Company, chartered by Charles II in 1672, which was given the exclusive right to conduct the English slave trade with West Africa.

The Royal African Company was a royal enterprise in the fullest sense. The Duke of York — the future James II — was its governor. Members of the royal family, aristocrats and City of London merchants were its shareholders. The company built and garrisoned a chain of forts and trading posts along the West African coast — most importantly Cape Coast Castle in what is now Ghana — and used these as holding stations where enslaved Africans could be assembled, inspected and loaded onto ships.

Between 1672 and 1713, the Royal African Company transported approximately 100,000 enslaved Africans across the Atlantic. Its ships were branded with the initials “DY” (Duke of York) and later “RAC” — a mark that was also branded on the chests of enslaved people as a mark of property. This branding — of both merchandise and people with the same initials — captures something of the trade’s fundamental character.

In 1698, facing pressure from independent merchants who resented the monopoly, Parliament opened the trade to all English merchants on payment of a ten per cent duty. The effect was explosive. Bristol, Liverpool and London competed to dominate the now-liberalised trade, each developing the infrastructure — the docks, the warehouses, the insurance markets, the banks — that made large-scale slaving possible.

The Key Players: Who Ran Britain’s Slave Trade

The British slave trade was not the project of a few villainous individuals. It was a system embedded in the economic and social fabric of the nation.

The port cities — Bristol, Liverpool and London — were its operational centres. Bristol dominated the trade in the late seventeenth and early eighteenth centuries; Liverpool overtook it by mid-century and became the world’s largest slaving port. By 1800, approximately forty per cent of the entire Atlantic slave trade passed through Liverpool. Merchants in these cities built fortunes, funded civic institutions, and were celebrated as pillars of their communities. Edward Colston of Bristol served as deputy governor of the Royal African Company and transported an estimated 84,000 enslaved Africans. He endowed schools, almshouses and churches with his profits. His name adorned a concert hall until 2020, when protesters threw his statue into the harbour.

The merchant class and its financiers were equally central. Insurers at Lloyd’s of London underwrote slaving voyages. Banks that would become Barclays and HSBC had connections to slave-trading wealth. The financial instruments developed to manage the risks and revenues of the trade — bills of exchange, marine insurance, credit networks — were foundational to the development of British financial capitalism.

African kingdoms played a complex and contested role. The slave trade could not have operated as it did without the participation of African rulers and merchants who captured and sold enslaved people to European traders on the coast. The Kingdom of Dahomey (in modern Benin) became one of the most active slave-trading states in West Africa, conducting annual raids into the interior to capture prisoners who were then sold to European traders at the coast. The Asante Empire in what is now Ghana was similarly active. The Kingdom of Benin, by contrast, largely refused to participate in the trade of its own people, though it continued trading other goods with European merchants.

This African participation does not relativise European responsibility — the demand that drove and expanded the trade was European, the ships were European, the plantations and their profits were European — but it complicates any account that presents the trade as something done entirely to Africa rather than with the collaboration of some African political actors.

The plantation owners of the Caribbean and American colonies were the trade’s ultimate beneficiaries. Sugar plantations in Jamaica, Barbados, Trinidad and Saint-Domingue (Haiti) were the most profitable enterprises in the Atlantic economy. A single plantation could generate annual returns that would take a labourer in England centuries to earn. The plantation system was maintained entirely by enslaved labour: men, women and children worked in conditions of extraordinary violence, under the threat of mutilation, torture and death.

The Middle Passage: The Crossing

The Middle Passage — the Atlantic crossing from the West African coast to the Americas — was one of the most systematic exercises in human degradation in recorded history.

Enslaved men were typically chained together in pairs, ankle to wrist, and packed below decks in spaces that allowed no room to sit upright. The standard allowance was roughly six feet by sixteen inches per person — less space than a coffin. Women and children were sometimes given slightly more room, which also made them more vulnerable to sexual violence from the crew. The holds were sealed during storms; in good weather, enslaved people were brought on deck to eat and to exercise — not out of humanity but to reduce the mortality rate that ate into profits.

The primary killers were disease: dysentery (sailors called it “the bloody flux”), smallpox, and a variety of respiratory infections spread rapidly through the overcrowded holds. On average, between ten and twenty per cent of enslaved people died during the crossing. On the worst voyages — and some were much worse — the mortality rate could reach fifty per cent or more.

Resistance was constant despite these conditions. Revolts aboard slave ships were more common than the historical record fully captures — merchants had incentive to suppress their documentation. Enslaved people refused food, jumped overboard, overpowered guards when they could. The Amistad revolt of 1839 and the revolt aboard the Zong before its notorious massacre are among the cases that entered historical record, but they represent a fraction of the resistance that occurred.

Why Britain’s Role Ended: Economics, Religion and Black Resistance

The abolition of Britain’s involvement in the slave trade — and eventually of slavery itself in British colonies — was not a single event but a decades-long struggle whose causes historians continue to debate.

The economic argument, advanced most powerfully by the Trinidadian historian Eric Williams in his landmark 1944 work Capitalism and Slavery, holds that abolition was possible only because the slave trade had become less economically vital to Britain by the early nineteenth century. The Industrial Revolution was creating new forms of profit that did not depend on enslaved labour; the sugar islands of the Caribbean were no longer as dominant as they had been; and free labour in the new industrial economy was increasingly seen by capitalist thinkers as more productive than enslaved labour. Williams’s argument remains influential and contested: other historians point to moral and religious factors as primary drivers.

The religious and moral campaign was mounted by a coalition that crossed class and denominational lines. The Quakers — the Religious Society of Friends — were among the first organised groups in Britain to condemn the slave trade as fundamentally incompatible with Christian principles. The Quaker-dominated Meeting for Sufferings began petitioning Parliament against the trade in 1783. In 1787, the Society for Effecting the Abolition of the Slave Trade was founded, with Granville Sharp and Thomas Clarkson as key figures alongside the Quaker network.

The campaign deployed the techniques of modern political activism: mass petitions (one 1792 petition bore 519,000 signatures — the largest petition in British history to that date), boycotts of slave-produced sugar, public lectures illustrated by models of the slave ship Brookes showing how enslaved people were packed, and a sophisticated pamphlet literature. Josiah Wedgwood, the pottery manufacturer, produced the iconic cameo showing an enslaved man in chains with the legend “Am I not a man and a brother?” — one of the most reproduced images in eighteenth-century Britain.

William Wilberforce was the movement’s parliamentary champion — articulate, well-connected, tireless in his advocacy. But he was one figure in a much larger coalition, and recent scholarship has been rightly critical of the tendency to place Wilberforce at the centre of a story that properly belongs to many thousands of activists, petitioners and above all to enslaved people themselves.

The Black abolitionists were among the movement’s most powerful voices. Olaudah Equiano’s Interesting Narrative (1789) — a first-hand account of kidnapping, the Middle Passage and the struggle for freedom — became a bestseller and shifted public opinion in ways that no white abolitionist’s writing could. Ottobah Cugoano’s Thoughts and Sentiments on the Evil of Slavery (1787) was even more radical, demanding immediate rather than gradual abolition and refusing to accept the racist assumptions that constrained even sympathetic white arguments. The Somerset case of 1772 — in which the judge Lord Mansfield ruled that an enslaved man brought to England could not be forcibly removed from the country — had established, ambiguously but importantly, that English law could not fully accommodate slavery.

The Haitian Revolution — the only successful slave revolt in history, which transformed the French colony of Saint-Domingue into the independent Black republic of Haiti in 1804 — profoundly altered the calculus of the debate. For British abolitionists, it was proof that enslaved people were human beings capable of self-governance and deserving of freedom. For slaveholders, it was a catastrophic warning of what might happen if enslaved people were given any cause to revolt. It accelerated the argument on both sides.

The Slave Trade Act 1807 and the Slavery Abolition Act 1833

The Slave Trade Act received Royal Assent on 25 March 1807, making it illegal for British subjects to participate in the slave trade. The vote in the House of Commons was 283 to 16 — by that point, the tide of public and political opinion had shifted decisively.

But the Act abolished the trade, not slavery. Enslaved people in British colonies continued to be held in bondage for a further twenty-six years. The campaign to end slavery itself was long and hard; slaveholders and their political allies fought it at every stage.

The Slavery Abolition Act 1833 received Royal Assent on 28 August 1833 and came into effect on 1 August 1834. It freed approximately 800,000 enslaved people across the British Caribbean, Mauritius, the Cape of Good Hope and a small number of other territories.

The terms of the Act reveal its politics with uncomfortable clarity. Slaveholders received £20 million in compensation — equivalent to approximately forty per cent of the Treasury’s annual income, and to roughly £17 billion in modern terms. The money was paid by the British taxpayer (via a loan that was not finally repaid until 2015). The enslaved people received nothing: no land, no capital, no back wages, no reparations. They were instead subjected to an “apprenticeship” system under which they were required to continue working for their former enslavers without pay for up to six years. The apprenticeship system was abolished in 1838 following sustained resistance from the formerly enslaved.

Legacy: A Debt That Has Never Been Settled

The wealth generated by the slave trade and slavery is woven into the fabric of British life in ways that are only now being systematically documented. The Legacies of British Slave-ownership database, compiled by researchers at University College London, has traced the direct financial links between slave-owner compensation payments and the institutional wealth of hundreds of British companies, families and institutions. The Caribbean sugar economy funded the development of banking (Barclays, Lloyd’s), docks, country houses, churches and universities. The industrial infrastructure of cities like Glasgow, Liverpool, Bristol and London was built in significant part on profits derived from enslaved labour.

This is not a completed history. The conversations about reparations, about the repatriation of cultural objects taken during the colonial period, about the teaching of colonial history in British schools — all of these are live political questions. The toppling of Edward Colston’s statue in Bristol in June 2020, and the debates that followed about whose image occupies public space, are symptoms of a reckoning with this history that British society has not yet completed.

Key Sources and Further Reading

• Thomas, H. (1997): The Slave Trade: The Story of the Atlantic Slave Trade 1440–1870, Simon & Schuster
• Williams, E. (1944): Capitalism and Slavery, University of North Carolina Press
• Olusoga, D. (2016): Black and British: A Forgotten History, Macmillan
• Hochschild, A. (2005): Bury the Chains: The British Struggle to Abolish Slavery, Macmillan
• James, C. L. R. (1938): The Black Jacobins: Toussaint L’Ouverture and the San Domingo Revolution, Secker & Warburg
• Equiano, O. (1789): The Interesting Narrative of the Life of Olaudah Equiano, published by the author
• Cugoano, O. (1787): Thoughts and Sentiments on the Evil of Slavery, published by the author
• Trans-Atlantic Slave Trade Database: slavevoyages.org (Emory University)
• Legacies of British Slave-ownership Database: ucl.ac.uk/lbs (University College London)