Between 1501 and 1750 something on the order of five million people were carried from Africa across the Atlantic as slaves, part of a traffic that reached 12.5 million embarkations before it ended. The trade grew slowly in the sixteenth century, when Portuguese and Spanish shipping predominated, then expanded sharply from the 1640s as Dutch, English and French planters developed sugar in the Caribbean and as Brazil's plantation economy grew; by the first half of the eighteenth century well over a million people were being shipped every twenty-five years. Captives were obtained through warfare, raiding, judicial enslavement and debt within Africa and sold at coastal factories to European carriers; the largest single source region was West Central Africa. Mortality on the Atlantic crossing averaged in the region of twelve to fifteen per cent over the period, falling over time, and further deaths occurred during capture, the march to the coast and confinement in barracoons, none of which appear in the shipping records. The Trans-Atlantic Slave Trade Database, which underlies all modern figures, is explicit that its totals are estimates extrapolated from documented voyages rather than a census.
Portuguese, Spanish, Dutch, English, French and Danish merchants, licensed by their states and supplied by African polities and traders, shipped captive Africans across the Atlantic to American plantations and mines
The Slave Voyages database reconstructs embarkations and disembarkations voyage by voyage, but the source populations were dozens of polities from Senegambia to Angola whose sizes over 250 years cannot be reconstructed; Manning's modelling of Atlantic Africa suggests populations in the tens of millions, but the deaths, dislocations and captures within Africa are not captured by any denominator. A percentage here would be spurious.
The lower bound is the implied number who died at sea before 1750: the database's own embarked and disembarked totals imply an average loss of roughly one captive in eight on the Atlantic crossing, which on four to five million embarkations gives something over half a million deaths in transit. The upper bound adds the deaths that occurred between capture and embarkation — in the wars and raids that produced captives, on the march to the coast and in coastal barracoons — which are not recorded in any source and are estimated by historians at a further fraction comparable to or greater than shipboard mortality. No count of the latter exists and every figure for it is an inference.
Chaining and confinement in barracoons and below decks, the shipping of children as a substantial minority of captives, sexual violence aboard ship and punishment regimes are documented in the shipping records, surgeons' logs, parliamentary inquiries and captives' own narratives that underlie the Trans-Atlantic Slave Trade Database.
Ghana, Angola, Barbados, Togo, Jamaica, Nigeria, United States of America