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8.6 — The Atlantic Slave Trade, Fully Accounted
The Trans-Atlantic Slave Trade Database is a research project that has assembled records of individual voyages from shipping registers, customs records, insurance documents and company ledgers across a dozen countries. It currently documents around 36,000 voyages.
From that record: approximately 12.5 million Africans were embarked on ships between 1501 and 1866, and approximately 10.7 million survived to disembark in the Americas.
Roughly 1.8 million people died at sea.
These are not estimates from impressions. They are counts from the traders' own paperwork, because the traders were businesses and businesses keep records. This chapter uses those records, and it should be read knowing that the primary source for the scale of this crime is the accounting of the people who committed it.
Why it happened
Sugar, principally.
Sugarcane requires a specific and brutal production process. The cane must be cut and crushed within a day or two of harvest or the sugar content falls, so the mill has to run continuously through the harvest. The boiling house operates day and night at extreme heat, and accidents — hands caught in the rollers, burns from the boiling syrup — were routine, which is why mills kept an axe by the rollers.
It is therefore a plantation crop: it needs a large workforce, working in coordinated shifts, under coercion, on a fixed schedule, in a tropical climate.
Sugar was also enormously profitable, because European demand rose without limit as prices fell — from a luxury spice in 1500 to an everyday commodity by 1800. Then tobacco, coffee, indigo, rice and finally cotton followed the same model.
Why enslaved Africans specifically
This is the question that matters, and the answer is a sequence of decisions rather than a single one.
Indigenous American labour failed because the population was collapsing from disease (Chapter 8.5), and because the survivors could escape into terrain they knew.
European indentured labour was tried extensively — a large proportion of early English migrants to the Caribbean and Virginia were indentured servants, and mortality among them was appalling. It failed as a system for three reasons: indenture is temporary, so the planter loses the worker after four to seven years; indentured servants had legal standing and could and did sue; and as English wages rose after the plague-era demographic shift and as conditions in the colonies became known, the supply dried up.
Enslaved Africans were chosen because the status was permanent and heritable, because a person who did not know the country could not easily escape, and because a supply already existed — West African societies had slavery and there were established trading networks.
And there is a grim epidemiological factor. Africans had substantially better resistance than Europeans to malaria and yellow fever — including through the sickle-cell trait (Chapter 3.8) and acquired immunity — and in Caribbean sugar colonies European mortality was catastrophic. Planters observed this and it entered their calculations.
Racial ideology came afterwards, not before. Slavery in the ancient and medieval world was not racial (Chapter 5.4) — it followed conquest, debt and birth, and Europeans enslaved Europeans, Muslims enslaved Muslims and Christians, and Africans enslaved Africans. The doctrine that Africans were naturally suited to slavery was constructed in the seventeenth and eighteenth centuries to justify a system that already existed and had become economically central. Colonial Virginia's statutes show the process in law: the 1662 act making a child's status follow the mother's, the 1667 act stating that baptism does not confer freedom, and the progressive hardening of racial categories over the following decades.
The African end
This has to be described accurately, because both the sanitised and the simplified versions get it wrong.
Europeans did not, in the main, capture people directly. Disease made the West African interior lethal to them (Chapter 3.8) — European mortality on the coast ran at extraordinary rates until quinine — and they lacked the manpower and the local knowledge.
They bought people, at coastal forts and trading posts, from African traders and rulers.
The supply came from war captives, from raids conducted for the purpose, from judicial condemnation, and from debt. The trade transformed African politics: states that could supply captives obtained firearms, and firearms enabled more raiding, which produced more captives. Dahomey, Asante and Oyo all expanded on this basis. The historians' term is the gun-slave cycle, and its existence is documented in the trade records.
This is not a mitigation and it is a fact. African participation was real, extensive and driven by the same incentives that drove everyone else in the chain. It also does not transfer responsibility, because the demand was European and American, the ships were European, the capital was European, the plantations were European-owned, and the scale — 12.5 million people over 350 years — was set by that demand. African polities that refused to participate, and some did, were undercut by those that did.
And some African rulers protested. Nzinga Mbemba, king of Kongo, wrote to the king of Portugal in 1526 complaining that Portuguese traders were seizing his subjects including nobles and members of his own family, that the country was being depopulated, and asking that the trade be stopped. The letters survive. The trade continued.
The demographic effect on Africa was severe and is measurable. Around 60 percent of those taken were men, which distorted sex ratios and social structures. Regions of heavy extraction show long-run consequences: Nathan Nunn's economic work found that the African countries from which most slaves were taken are, on average, the poorest today, and that the relationship holds after controlling for the obvious alternatives. The proposed mechanism is the destruction of trust and of state-building — when your neighbour might sell you, you do not build institutions with your neighbour.
The Middle Passage
The crossing took six to twelve weeks.
People were held below deck in spaces typically under a metre and a half in height, chained in pairs, lying on their sides, with barely room to turn. They were brought up in shifts for air and forced to exercise when the weather permitted.
Sanitation was effectively absent. Dysentery — called the bloody flux — was the largest single killer, along with smallpox, measles and dehydration.
Mortality on the crossing averaged around 15 percent across the whole period, falling somewhat in the later era as voyages got faster, and reaching far higher on individual voyages.
Resistance was constant. Insurrection attempts are documented on roughly one voyage in ten, and the security costs they imposed — extra crew, netting, chains — were a standard line in the accounts. Suicide by jumping overboard or refusing food was common enough that ships carried the speculum oris, a device for forcing the mouth open.
The Zong case, 1781, is the one that should be known. The crew of a British slave ship threw 132 living people overboard and the owners then claimed the insurance on them as lost cargo. The case reached an English court — not as murder, but as an insurance dispute. The publicity it generated, driven by the formerly enslaved abolitionist Olaudah Equiano and the campaigner Granville Sharp, was a significant moment in British abolitionism.
Where they went, and what happened there
The distribution is not what most people assume.
| Destination | Approximate share of arrivals |
|---|---|
| Brazil | ~46% |
| British Caribbean | ~11% |
| Spanish Americas | ~11% |
| French Caribbean | ~11% |
| Dutch Americas | ~5% |
| British North America / United States | ~4% |
Brazil received nearly half, and North America under 5 percent.
And there is a demographic fact that follows from this and requires stating. The enslaved population of British North America grew by natural increase; the populations of the Caribbean and Brazil did not, and had to be continuously replaced by new arrivals. The reason is that sugar plantation labour killed people faster than they reproduced. So the region that imported the fewest ended up with the largest enslaved population by 1860 — around 4 million in the United States — which is a statistic about relative brutality, not about relative humanity.
Life expectancy on Caribbean sugar estates was measured in years after arrival. The economic calculation, stated in planters' own manuals, was whether to work a person to death and replace them or to maintain them.
Abolition
Why it ended is genuinely argued and the honest answer involves several forces.
The moral campaign was real and it was the first modern mass political movement. British abolitionism from the 1780s — Quakers, evangelicals including Wilberforce, and the formerly enslaved including Equiano, whose autobiography was a bestseller, and Ottobah Cugoano — invented the techniques: the petition campaign, the consumer boycott of slave-grown sugar, the mass-produced emblem, the parliamentary lobby and the atrocity image. The Brookes diagram is the ancestor of every campaigning graphic since.
Resistance by the enslaved was decisive and is systematically underweighted. The Haitian Revolution (Chapter 10.5) destroyed the richest colony in the world and demonstrated that the system could be overthrown, which changed the risk calculation everywhere. Maroon communities in Jamaica, Suriname and Brazil fought successful wars and won treaties. Revolts in Barbados in 1816, Demerara in 1823 and Jamaica in 1831 directly accelerated British emancipation, which came in 1833, two years after the Jamaican rising.
Economic arguments existed and their weight is contested. Eric Williams argued in 1944 that slavery was abolished when it ceased to be economically essential, and that industrial capitalism found free labour more efficient. Later research has substantially challenged this — the British Caribbean was still profitable at abolition, and Britain gave up a valuable trade. The current balance of scholarship gives more weight to the moral campaign and to slave resistance than Williams did, and his point that abolition served industrial Britain's interests better than it served the planters' has force.
The timeline. Britain abolished the trade in 1807 and slavery in its colonies in 1833. The United States banned the trade in 1808 and abolished slavery in 1865 after a civil war. Brazil abolished in 1888, the last in the Americas. The illegal trade continued into the 1860s, and the British West Africa Squadron intercepted ships and freed around 150,000 people over sixty years.
And the compensation deserves stating. When Britain abolished slavery in 1833, it paid £20 million in compensation — around 40 percent of the annual national budget — to the slave owners. The enslaved received nothing and were required to serve a further period as "apprentices". The loan raised to pay that compensation was finally paid off by the British taxpayer in 2015.
The other slave trades
Completeness requires naming them.
The trans-Saharan and Indian Ocean trades moved an estimated comparable total over a much longer period — roughly the seventh to the twentieth century — with different patterns: a majority of women, destined for domestic and concubine roles, and widespread castration of male captives with very high mortality. The estimates are far less reliable than the Atlantic figures because the record-keeping was not commercial in the same way.
Slavery existed in nearly every historical society in this volume, including in India, where various forms of bondage and untouchability-adjacent servitude were widespread and where the British formally abolished the legal status in 1843.
Stating this is not whataboutery if it is done correctly. The Atlantic trade was distinctive in three respects: its scale in a short period; its racialisation, which produced a hereditary caste defined by ancestry; and its integration into an industrial-scale commercial economy with shipping, insurance, credit and futures markets built around it.
Where this shows up in your life
The demographics of the Americas — Brazil has the largest population of African descent outside Africa.
Music. Blues, jazz, gospel, samba, rumba, reggae, and everything descended from them, which is most of the world's popular music.
Institutions built on it. Several British banks, insurance firms including Lloyd's, and universities in Britain and the United States have documented endowments and origins connected to slavery, and a number have published investigations and made restitution commitments in the last decade. The University College London Legacies of British Slavery database lists the individual recipients of the 1833 compensation payments and is publicly searchable.
And the argument about reparations is a live political question in the Caribbean, in the United States, in Britain and at the United Nations, and it is conducted with reference to exactly the records this chapter uses.
What the next page covers
While the Atlantic system was being built, Europe spent a century and a half killing itself over the interpretation of the Christian sacraments. Chapter 8.7 covers the Reformation and the wars of religion — what Luther actually objected to and why printing made it unstoppable, what Calvin's theology did to economic life, how England's reformation happened for entirely different reasons, and how the Thirty Years War killed perhaps a third of the German population and ended with a peace treaty that invented the modern international system.