What did Sabará, Minas Gerais and Baltimore, Maryland have in common? At first glance, not much. Sabará flourished as a booming gold-mining town in the first half of the eighteenth century and relied on the labour of thousands of slaves by 1750, when Baltimore had a total population of 200. The North American town developed in the latter half of the century as a commercial and ship-building centre, but still trailed Sabará in size by the end of the century. Located deep in Brazil's interior, Sabará lacked connection to major Atlantic trading routes, while Baltimore enjoyed direct access to the sea. Whereas in 1810 only 10 per cent of Baltimore's population was enslaved and another 12 per cent consisted of free or freed blacks and mulattos, in Sabará a third were enslaved and over half free or freed.

Yet Professor Dantas makes an excellent case for the comparability of these two urban centres and the role played by Africans and their descendants in their respective transformations. In both towns the labour of slaves was key to economic growth. In an urban environment with diversified economic activities, slave owners required workers to labour without constant supervision and therefore to exercise both skill and individual initiative. To this end slave owners granted or promised freedom to many, and used the example of the freed to encourage the labour of the still enslaved. Both cities ended up with a larger proportion of free and freed blacks and mulattos than other cities in their respective countries. In this way, non-whites gained significant leverage.

Having established comparability, Dantas turns to the differences. A common practice in Sabará was to let slaves find their own work for a wage, returning a fixed amount to their owners on a daily or weekly basis. Any surplus was the slave's to keep, and so the possibility existed of saving enough to buy their freedom. In Baltimore it was much more common to convert the slave's status to that of an indentured servant for a fixed term of years. As for outright manumission, men were much more frequently freed in Baltimore than were women, while in Sabará the situation was reversed, cascading into a greater number being born free in the Brazilian city. Slave children in Sabará had a much higher chance of being freed than those in Baltimore. A far wider range of occupations was open to the free-born in Sabará, and these even included participation in the officially sanctioned civilian militia and positions in the state bureaucracy. The freed in Sabará even came to own slaves of their own, a situation rare in Baltimore.

Racial ideology in the two towns also diverged. Dantas is careful not to exaggerate the degree of difference, but clearly the place of mulattos in Sabará contrasted sharply to that in Baltimore. This contrast begins in the record-keeping itself, where Baltimore mulattos were not usually distinguished from other blacks. When they were, documents show that mulattos were not more likely to be freed than blacks, in contrast to the situation in Sabará. Interracial marriage – as distinct from sexual union – was virtually unknown in Baltimore, but it was not unusual for whites to marry mulattos in Sabará. And more: in Baltimore the occupations open to free persons of African descent did not differ radically from that of slaves, regardless of the lightness or darkness of the individual's skin, in contrast to the distance that separated the free from the slaves in Sabará, especially in the case of mulattos.

When it comes to explaining the differences, Dantas does not extend her reach as far as she might; perhaps she took some possible explanations as self-evident. By concentrating so exclusively on Africans and their descendants, she pays little attention to the much greater presence of white workers in Baltimore over Sabará, mentioning them only a couple of times almost as an aside and never explaining their availability. Abolitionist sentiment in Baltimore and its almost total absence in Sabará is mentioned in passing but not explored. Yet residents of Sabará would surely have been astounded to learn that in 1783 the state of Maryland outlawed the importation of slaves from other states, a measure that was not adopted anywhere in Brazil until a century later. Political and religious ideas diverged in these two cities and could have been more directly analysed and dissected than they are on pp. 112–14. In the end, one is left to wonder how comparison per se elucidates the history of either place in ways we would not otherwise have seen.

A challenge frequently confronted in writing comparative history is the disparity in the nature of sources. Brazil presents the investigator with an enormous wealth of post-mortem inventories but a relative absence of diaries and letters, and, for the eighteenth century, a total absence of newspapers and other contemporary printed materials. The situation in Baltimore is the opposite, and also includes more tax records and household censuses. The units of analysis may also differ: the Brazilian município included a vast expanse of rural land, and Dantas does not draw all her numbers from the strictly urban space to which she alludes. This probably explains the marked disparity between the figures she presents for Sabará's total population and those referred to by historian Francisco Vidal Luna in his work.

Dantas' research in primary sources for both Sabará and Baltimore is deep and thorough, and her knowledge of the historiography of the two countries concerned is astonishing. She has combed through hundreds of probate and baptismal records, freedom charters and other primary materials. Her approach is primarily quantitative, but she skilfully weaves stories of individual experience into her account, drawing in the reader. I would have appreciated an appendix that presented some of the principal quantitative data in a single table rather than only as text or in small tables, some of which are difficult to understand, but this is a small complaint. The author's prose is clear and accessible, and she has substantially increased our understanding of slavery and manumission in these two Atlantic-world cities.