Extending the Frontiers is a product of the heated debate provoked by Philip Curtin's The Atlantic Slave Trade: A Census (Madison: University of Wisconsin Press, 1969). A brief historiographical context is, therefore, pertinent. The debate started in 1975, when a young scholar, Joseph E. Inikori, found himself in an unexpected battle with the author, Curtin, in a Colby College conference that year. This was followed in 1976 by the publication of Inikori's article and the three-way discussion it generated (“Measuring the Atlantic Slave Trade: An Assessment of Curtin and Anstey.” Journal of African History 17, no. 2 [1976]: 197–223; no. 4, [1976]: 595–627).

A turning point in the debate was reached in 1998, when a conference was held in Williamsburg, Virginia, to celebrate the production of a database by David Eltis, David Richardson, and others, presented as a confirmation of Curtin's estimate of the overall volume of the Atlantic slave trade. The database was published in 1999 (David Eltis et al. [eds.], The Transatlantic Slave Trade: A Database on CD-ROM [Cambridge: Cambridge University Press, 1999]). Eltis and Richardson used this database to publish a number of articles strongly confirming the Curtin's estimates (David Eltis, “The Volume and Structure of the Transatlantic Slave Trade: A Reassessment.” William and Mary Quarterly, 3d Series, Vol. I.VIII, no. 1 [2001]: 17–46; David Eltis and David Richardson, “Prices of African Slaves Newly Arrived in the Americas, 1673–1865: New Evidence on Long-Run Trends and Regional Differentials.” In Eltis et al. [eds.], Slavery and the Development of the Americas [Cambridge: Cambridge University Press, 2004]: 181–218).

Mounting criticism by specialists in the field led to the production of a second database upon which Extending the Frontiers is based. As Eltis and Richardson explain, research done by others (2001–2005) “resulted in the discovery of 8,232 additional slave voyages that we were not aware of in 1999” (pp. 6–7). These newly discovered slave voyages constitute 30.2 percent of the 27,233 slave voyages in the 1999 database. On the shipment of captives, Eltis and Richardson's new assessment yields a grand total of 12,521,334 captives transported from Africa and 10,702,656 landed in the Americas. Compared with Curtin's estimates, the export figures are 13.8 percent more than the 11 million scholars generally derived from those estimates, and 13.2 percent greater than Eltis and Richardson's estimates derived from the 1999 database; the new import assessments are 11.9 percent larger than Curtin's. Readers who have followed this heated debate since the 1970s will agree that this reversal of fortune for the Curtin's estimates is entirely contrary to expectations built up in the literature for several decades. But there is more to Extending the Frontiers.

There can be no doubt that the new database offers a very large sample of voyages in the Atlantic Slave Trade. For thousands of these voyages, the amount and range of information in the database provide a solid foundation for the study of several aspects of the Atlantic Slave trade and even Atlantic world history. For example, 13,253 voyages contain information on the size of the crew on at least one of the legs of each voyage; information on place(s) of captive embarkation in Africa and disembarkation, 26,939 and 28,985 voyages, respectively; information on age or gender of Africans disembarked, 3,570 voyages; evidence on shipboard revolt by captives or attacks by shore-based Africans, 530 voyages; and more (table 1.1, p. 9). The wide-ranging information in this large sample is employed by several authors to examine a number of pertinent issues in the essays included in the volume. Apart from the overall size of the trade reassessed by the editors, already mentioned, five essays focus on origins and destinations of the forced migrants; three are devoted to the trade conducted by the French, the Dutch, and northern Germany; and the last three focus on “some wider consequences and implications of the new data.” These are all fine essays. Individually, they make important contributions to the literature on the subjects examined. Specialists in the field are likely to find new issues that the data assembled will help to raise for detailed study. To make the new database even more valuable to specialists, it is available on open access at http://www.slavevoyages.org. This is certainly a useful source for scholars in the field, including Atlantic world historians.

Much of this otherwise excellent work of historical scholarship, however, is tainted by the unfathomable attempt by the editors, Eltis and Richardson, to mislead the reader on the issue of the overall number of captives shipped from Africa and landed in the Americas. “It may seem that the major thrust of the research presented here,” they opine, “is to add weight to Curtin's critics.” Continuing, they write: “This is, of course, a central part of the present volume, although we expect that the Hernaes and Inikori estimates of close to or in excess of 13 million transported slaves are too high to find support in voyage-based evidence” (p. 53). Hernaes's work and his estimate, 12.8 million, are shown (p. 5); but Inikori's estimate and where to find it are not stated by Eltis and Richardson. The reader is simply asked to believe that it is “too high to find support.” The Inikori estimate in question is 12,689,000 and it was in a paper presented in the 1998 Williamsburg conference organized by Eltis, Richardson, and others, mentioned earlier. The paper, entitled, “The Known, the Unknown, the Knowable, and the Unknowable: Evidence and the Evaluation of Evidence in the Measurement of the Transatlantic Slave Trade,” was published in a volume edited by Toyin Falola (Ghana in Africa and the World: Essays in Honor of Adu Boahen (Trenton, NJ: Africa World Press, 2003); see p. 536 and note 8, p. 560, for the estimate).

The Inikori estimate is only 1.3 percent larger than Eltis and Richardson's new estimate of 12,521,334; the Hernaes estimate is 2.2 percent higher. To say that these differences are too large for Inikori and Hernaes to find support must mean that Eltis and Richardson believe that the margin of error for their estimate is zero. Given the nature of the evidence, such a claim is as unwarranted as the one made by Philip Curtin in 1969, that “while it is doubtful” his estimates “are too low, it is easily possible that they will be too high” (Curtin, Census, p. 86). It is significant to note that while the number of newly discovered slave voyages (8,232) is 30.2 percent of the number known in 1999 (27,233), as mentioned earlier, Eltis and Richardson's new estimate of the total number of captives shipped from Africa is only 13.2 percent more than their earlier estimate derived from the 1999 database. Need it be said the weaknesses noted here are damaging to the credibility of the estimates of the overall size of the Atlantic slave trade presented in this volume by Eltis and Richardson. Suffice it to add that there is much that is valuable in the new database and the essays based on it, the blemish in the overall size of the slave trade estimated by the editors notwithstanding.