The history of the Atlantic World and of the transatlantic slave trade, especially, has for too long focused on the commerce conducted north of the equator. The slave colonies of the Caribbean and the emergence of the US still dominate the historiography of not just slavery and the slave trade, but the demographic and political history of the Americas. In the last decade, scholarly contributions to the history of the South Atlantic have begun to redress this situation, but even a cursory examination of the titles in the annual survey of the literature in the journal, Slavery and Abolition, indicates that the imbalance is still pronounced. Terms such as the “Middle Passage” predominate, even though, given the out and back nature of the massive trade to Brazil, most of it under the Portuguese flag, a “middle passage” simply did not exist. Scholars still fail to recognize that Rio de Janeiro and Bahia de Todos os Santos (now Salvador) and quite possibly Pernambuco (now Recife), each dispatched more vessels to Africa to obtain slaves than did any of the ports of Liverpool, London, Bristol, and Nantes that still predominate in the extensive English, Dutch, and French language scholarship on this subject. Scholars of the slave trade in the Indian Ocean refer to the “tyranny of the Atlantic World” to explain the imbalance of research funding dedicated to slave trading in the two oceans, when an equally drastic imbalance is one within the Atlantic—that between the still predominant North and the South Atlantic.

Patricia Seed’s new book, Sails and Shadows: How the Portuguese Opened the Atlantic and Launched the Slave Trade (2026), is ostensibly about a slave trading system anchored in Western Europe. Her argument about the foundational role of the Portuguese in not just establishing a transatlantic slave trade but in opening up the oceans of the world to European voyagers makes for a compelling read. It establishes the Portuguese creation of a body of oceanic knowledge and links with African peoples that other maritime nations were never quite able to match. While the broad outlines of the early Portuguese transoceanic ventures will be familiar to most readers, Seed’s new book combines a total familiarity with the primary sources with an impressive knowledge of the data and insights now available from the modern sciences—particularly of climatology. The book provides a model for how the insights of these new disciplines can enrich the writing of even well-known historical events.

But the book is not just about navigating the oceans. It provides a basis for reassessing the Portuguese role as the dominant European slave trading nation. Early chapters entitled “How trading replaced conquests” and “How Enslaved Interpreters Established Trade” identify the unique features of the Portuguese relationship with Africans. Other European countries had their own navigators who in a few short decades latched on to the knowledge pioneered by the fifteenth-century Portuguese mariners. But over the course of nearly four centuries of Atlantic slave trading and the extraction of nearly thirteen million enslaved Africans from the subcontinent, no other nation came close to replicating the close and frequently tense relationship with African polities that underpinned the Portuguese position as the leading European slave trading nation. What we have here is an explanation not just of the Portuguese conquest of the oceans, but why and how the Portuguese created a transatlantic trading system that survived for almost four centuries.

While the book does not go much beyond the fifteenth century, it nevertheless provides a key insight into the subsequent dominant and still poorly recognized Portuguese role in the slave trading business. The key for Seed is what she calls “soft power” at the core of which was the practice of cultivating what might be termed diplomatic alliances, reinforced with gifts of merchandise, but above all underpinned by a drive to come to terms with a dizzying range of African languages that remained unique among Western European nation-states. From the very outset of their ventures into Atlantic Africa, the Portuguese brought family members of African rulers to Lisbon, where they could learn about the bigger picture of the business and, of course, the Portuguese language. Within Africa itself, Portuguese merchants learned African languages and married into ruling families. The offspring of such unions often became major slave traders, and later, especially in Angola, Portuguese speakers attempted to build supply networks in the far interior. Often precarious and temporary, these links were never reproduced on the same scale by their European competitors. There were, of course, other instances of European nationals building networks within Africa. A point that she does not make, given that her remit ends in 1640, is how the Portuguese transatlantic system endured into the nineteenth century. Her book begs the question of how this small country could dominate the slave trade—except for six decades of British preeminence in the late eighteenth century. Larger and richer nations, including the British, could never match the Portuguese soft power that sustained their position in Africa until the late nineteenth century.

In a real sense, the Portuguese not only initiated the transatlantic system, but they were also the last to leave it. One of the last Courts of Mixed Commission established in the nineteenth century to adjudicate vessels suspected of slave trading was located in Luanda, Angola, in the 1850s. It had two judges, one British and one Portuguese, with two auxiliaries. Unbeknownst to the British pair, their Portuguese counterparts were actively involved in the transatlantic business while serving as anti-slave trade officials. In this case, not in owning slave ships, though that too was possible, but rather in supplying captives to vessels destined for Cuba. So Portuguese engagement was able to survive even the close scrutiny and impact of British attempts to suppress the transatlantic business. Clearly, the final traffic to Cuba, as with the sixteenth-century traffic, was still largely in Portuguese hands, at least in the acquisition and transmission of enslaved people.Footnote ¹ Over nearly four centuries, no other nation could come close to emulating the networks that the Portuguese established in Africa. These were not based on military power but rather the self-interest of buyers and sellers of slaves, often involving the offspring of European-African marriages.

Why is it that the Portuguese were able to survive the intervention of much wealthier European competitors—first the Dutch, then the English and the French—when maritime skills, specifically navigational knowledge, came to be shared quickly across all European nations? Picking up this new sea-going expertise proved much easier than reaching out to slave traders within Africa. But the unique networks that the Portuguese established within Africa and described so well by Patricia Seed provide only part of the answer. Recent research has focused on the organization of transatlantic slaving expeditions in the South Atlantic, elements of which were just not to be found among their better-known Western European competitors mostly operating in the North Atlantic. Slave ships leaving Liverpool, Middelburg, or Nantes would always have a clear distinction between owners of a vessel and the people hired to work on the ship—the traditional division between capital and labor. The countries with the most sophisticated capital markets—the Dutch and the English, especially—each came to briefly dominate the business, and to an even greater extent, the subsequent historiography of the transatlantic slave trade.Footnote ² But no such clear-cut division between capital and labor characterized Portuguese involvement in the traffic, not just in the slave trade but in most long-distance commerce down to the late nineteenth century.

The Portuguese continued to use a financing system typical of medieval trade in Europe and the Mediterranean and indeed common in the world beyond. This was the “commenda” arrangement, which at root was a partnership between two merchants—a senior party based in Europe, typically with a majority stake, and an often geographically remote junior with a minority interest. In the hands of the Portuguese, even crew members could be recruited in this system so that they effectively had an interest in the voyage or, more specifically, individual captives below deck, rather than receiving wages. The dividing line between capital and labor thus largely disappeared on Portuguese voyages, and with it came a reduced need to raise capital. This was in sharp contrast to the British, French, and Dutch voyages, where investors had quickly adopted the corporate model about the time these countries got involved in the transatlantic traffic. Seed does not address the question, but commenda partnerships were prevalent not only in the earliest Portuguese voyages into the Indian Ocean and beyond but also among merchants—Muslim and Indian—where commenda contracts were widely used in engaging with each other into the twentieth century. Portugal did eventually create companies specifically to engage in the slave trade, but these never replaced the commenda partnership model that remained in use through the nineteenth century. In the context of the Atlantic slave trade, such arrangements allowed merchants in Bahia and other Brazilian and Portuguese ports to compete successfully with slave traders based in North America and Europe, where individual merchants operating in a capital abundant environment formed corporate partnerships.Footnote ³ The clear distinction between owners and employees everywhere in the North Atlantic and clearly apparent in the British, US, Dutch, and French slave trades becomes blurred in the Portuguese case.

Patricia Seed’s impressive and very readable book is of course complete on its own terms. But it can nevertheless be read in addition as providing at least half the explanation for Portuguese preeminence over most of the four centuries of slave trading in the Atlantic world, despite her remit being just the early years of Portuguese involvement. Like the Spanish in the Americas, the Portuguese, as Seed explains, were the first to interact with sub-Saharan Africa and were able to select and retain the most productive locations for trade in the subcontinent. For them, it was the trade in people, in the Spanish case, the trade in silver. In the absence of abolition and British withdrawal from the trade in 1807, perhaps the corporate model of organizing a slaving expedition would have finally become predominant. On the other hand, nothing could have replaced the soft power system of the Portuguese that this book describes so well. Perhaps the tyranny of the North Atlantic is at last beginning to wane.