One significant and possibly surprising fact about the Atlantic slave trade, the massive human-trafficking business that shipped more than 10 million Africans to the Americas between 1501 and 1867, is the small role of the United States in it. About 400,000 Africans were loaded onto slavers and shipped to Virginia, South Carolina and other North American destinations, but this was less than 5 percent of the total. About 3.5 million Africans were shipped to the Caribbean (Barbados, Cuba, Haiti and elsewhere) and almost 4.9 million to Brazil. Nor was the United States a leading player in the traffic itself. While about 300,000 Africans crossed the Atlantic in US-owned ships, 1.1 million crossed in Spanish vessels, 1.4 million in French ships and 3.3 million in British ones. Precisely because of Brazil’s leading role as a slave trade destination, the Portuguese topped this list as well: Portuguese-owned slavers carried 5.8 million Africans across the Atlantic.

These larger and smaller numbers, of course, have no moral significance. Even the lower figures are shockingly high. But even if they weren’t, the relevant crime was any participation in the slave trade—or slavery itself—rather than some degree of participation. Still, as historian David Eltis explains in Voyages: The Trans-Atlantic Slave Trade Database, a monumental trove of information publicly available online, the most striking point about the morality of the slave trade was that, for most Europeans, "the shipping of enslaved Africans across the Atlantic was morally indistinguishable from shipping textiles, wheat, or even sugar." Americans of European descent did not think any differently. From Rhode Island to Rio de Janeiro, slaving was usually treated as a legitimate business that built respectable commercial fortunes.

There have been some striking modern reckonings with this history. Brown University, founded and endowed by prominent Rhode Island slave-trading families, established a Steering Committee on Slavery and Justice in 2003 that was charged, according to its 2006 report, with examining not only "the University’s historical entanglement with slavery and the slave trade" but also "the complex historical, political, legal, and moral questions posed by any present-day confrontation with past injustice," a reference to the thorny problem of whether and how to pay reparations to African-Americans for the injuries and injustices of slavery. The report presented a great deal of research, ranging well beyond Rhode Island slave trading to the larger history of American racial oppression and worldwide efforts to cope with past injustices (reparations, prosecutions, truth commissions). While its conclusion was anticlimactic and even somewhat self-serving—"If this nation is ever to have a serious dialogue about slavery, Jim Crow, and the bitter legacies they have bequeathed to us, then universities must provide the leadership"—its intellectual earnestness and moral sincerity are beyond reproach.

In 2007 Britain commemorated the bicentennial of its abolition of the slave trade on a lavish scale, spending $20 million on programs across the country, ranging from the solemn and scholarly (museum exhibits, public lectures, theatrical works) to the more or less fanciful (a school project intended "to celebrate the abolition of the transatlantic slave trade and encourage community cohesion" by developing a nature trail and erecting a freedom statue). Kicking off the proceedings, Prime Minister Tony Blair embraced the anniversary as an opportunity "not just to say how profoundly shameful the slave trade was" and "rejoice at the different and better times we live in today" but to propose increased aid to Africa, celebration of African and Caribbean contributions to British culture, eradication of continuing racism in Britain and a campaign to end modern slavery and human trafficking. The US version of this commemoration a year later (the United States banned slave importation in 1808, the first opportunity under the slave trade clause of the Constitution) was more muted; although Congress passed a law "to ensure a suitable national observance," it stripped the funding before passage. President George W. Bush did not participate.

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The public business of commemoration aside, the real question—the difficult question—is, What kinds of things do nonspecialists actually want to know about the slave trade? Adam Hochschild’s Bury the Chains: Prophets and Rebels in the Fight to Free an Empire’s Slaves (2005) is a stirring history of the first wave of the British abolition movement—accurate, responsible and sophisticated—but with a heroic plotline not unlike that of the biopic Amazing Grace (2006), in which a dashing young William Wilberforce (played by Ioan Gruffudd) sacrifices his health to steer slave trade abolition through Parliament, aided by the scenery-chewing Albert Finney (as the reformed slave ship captain John Newton, who wrote the hymn) and Michael Gambon (as the politician Charles James Fox). Marcus Rediker’s The Slave Ship: A Human History (2007), meanwhile, is a horrifying account of the everyday torture and murder at the heart of the slave trade, epitomized by the sharks that followed slave ships to feast on the plentiful corpses of its victims.

The Voyages database is not like Bury the Chains or The Slave Ship. There is nothing romantic about it, but its horror arises only through the cumulative weight of its abstract pieces of information: names of ships and their owners and sailors; voyage itineraries and commercial outcomes; the numbers of enslaved Africans on each ship with the places where they were bought in Africa and sold in the Americas; the percentages of men, women and children in the "cargoes"; the numbers who died on the voyages; and records of revolts and other acts of open resistance. Users can sort, tally, map and graph the data in various ways, such as choosing the voyages from particular years or longer periods, the voyages of ships of particular sizes or flying under particular flags, the ones that sailed from or to particular places, the ones on which revolts occurred and so on. Individual voyages can be studied in detail and identified through searches on the various characteristics of the voyages. With an interface that is fairly easy to navigate, the Voyages database is open to anyone for any reason: for scholarly research, idle curiosity or anything in between.

This project, an international collaboration led by Eltis of Emory University and David Richardson of Hull University in Britain, is a remarkable scholarly accomplishment. Since its origin in 1990, when Eltis and Richardson were studying the British slave trade and shipping business, it has expanded to embrace the voyages of French, Spanish, Portuguese and other Atlantic slavers. The project’s researchers proceeded to unearth thousands of previously unknown slaving voyages in business archives, newspaper files and personal correspondence. They also collated and standardized the records that earlier studies had gathered, mostly for single countries, to create one huge database for the slave trade as a whole. In 1999 the project published a CD-ROM with 27,233 voyages, which has been an essential source of data for historians such as Rediker. Since 1999 new research in Luanda, Havana, Lisbon and Madrid (and other places) has expanded the database to almost 35,000 of these murderous crossings. How murderous were they? About 12.5 million Africans were loaded onto slave ships; about 10.7 million emerged alive.

In addition to documenting the voyages, the website includes other kinds of information. An Estimates database tries to correct for gaps in the documentary records by roughly calculating the actual volume of the slave trade, as a whole and in subsets by time period, origin, destination and so on. Users can categorize the data and view or download the results in tables, maps and timelines. An Images database collects digitized manuscripts such as ship registers, along with paintings, drawings, engravings and maps. Another database identifies 67,000 Africans by name along with their regional origin, age, sex, height and destination. This Names database was constructed from the registers that British navy officers made in the nineteenth century when they intercepted slave ships and brought them, especially, to Freetown, Sierra Leone. The website also features interpretive essays about the history of the slave trade and, for teachers, a series of lesson plans in history, social studies and geography.

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The database has recently taken a fixed and smaller form. Atlas of the Transatlantic Slave Trade is a handsome volume—of coffee-table dimensions—that contains 189 colorful maps documenting, mostly, flows of slaves from African ports to the Americas. It also contains helpful essays by leading historians, telling quotations from slave trade participants and lavishly reproduced illustrations of artifacts: ship drawings, pages from ship registers, photos of shackles and instruments of torture, paintings of Caribbean plantations and lists of sick or dead Africans from slave ship captains.

But the work is an atlas above all, and its overwhelming purpose is to illustrate numbers. These numbers begin as straightforward statistics, such as what proportion of the 12.5 million captives left each of the major regions of Africa, marked with larger and smaller circles and the numbers, of which the most impressive is the 45.5 percent of the total who were shipped from ports in West Central Africa (mainly modern Angola and Congo). Then there is a map marking the destinations of the 10.7 million survivors, with the biggest numbers in Southeast Brazil (21.5 percent) and Bahia (14.7 percent), followed by Jamaica (9.7 percent), Pernambuco (8.1 percent, the third of the three Brazilian destinations), Cuba (7.4 percent), St. Domingue, modern Haiti (7.3 percent) and smaller figures for the other American destinations, with inset text reminding us that fewer than 4 percent disembarked in the United States.

Then things turn more complicated. Three maps examine the nationalities of the slave vessels that departed from particular African regions in particular periods, linking African regions of origin to American destinations with wider and narrower arrows and estimates of the populations transported. The next seven show origins and destinations by ownership of vessels, mapping the Spanish, the Portuguese and Brazilian, the Dutch, the British, the French and then the smaller North American and Baltic (mainly Danish and German) slave trades.

The next series, of thirty-one separate maps, shows in which ports the slave ships were outfitted and then maps the numbers of captives that ships from these ports took from regions of Africa to destinations in Europe and the Americas. Thus, for example, one map uses arrows of various sizes to show the numbers of captives that slave ships outfitted in Bristol took, both from each African region and to each American destination, adding an inset sketching the history of Bristol’s role in the slave trade. Other maps do the same things for, among other ports, London and Liverpool, Nantes and Bordeaux, Recife and Rio de Janeiro, Lisbon, Copenhagen, Havana and, of course, the port towns of Rhode Island.

The Atlas goes on like this, with one colorful data-filled map after another, each attesting to the monumentality of the Voyages research effort. After a while, though, the rationale for this combination of massive scholarship and lavish presentation starts to look very puzzling. What do you know when you know the home ports of the ships that carried the 2.8 million captives who left from Luanda and the American destinations of the 2.4 million who survived the trip? You know that Portuguese and Brazilian slavers dominated the trade at that African port, carrying their captives mainly to Brazil. The Atlas documents similar relationships for Gambia (mostly British ships, and Caribbean and North American destinations) and for twenty-five other African ports, some broken down into separate time periods (e.g., for Bonny, from 1659 to 1807 and from 1808 to 1838). It is clear that scholars, creative writers and some other interested readers will use the data to construct stories and social histories that will continue the work of bringing the transatlantic slave trade and all its horrors to life, but it is less clear that they are likely to use the Atlas for this purpose, as opposed to culling the data using the online Voyages database (for free).

The fact that the Atlas is priced at $50—dirt cheap for an elaborately designed coffee-table volume—may well increase its sales. While it is a little hard, at least for me, to visualize the audience who will want to keep it for casual perusal in the living room, it is easy to imagine the young people who might stumble across copies shelved in schools or home libraries. Like the old Time-Life books, the Atlas can inspire historical imagination and, most immediately, direct the curious to the Voyages database. All manner of further inquiries might be prompted by learning that the African populations shipped to the Caribbean included many more children after 1808 than before, by seeing the patterns of human and economic connection in the globalized worlds of previous centuries and by coming to fathom the terrible magnitude of the Atlantic slave trade.