Slavery, Sovereignty, and Empires: North American Borderlands and the American Civil War, 1660–1860

In the century framed by the Seven Years’ War and the American Civil War, the United States forged a vast but contested empire for slavery on the North American continent. In 1760, plantation slavery on the North American continent was confined to Britain’s five southernmost colonies. And while Britain, Spain, and France vied for dominion on the North American continent, Native Americans continued to control the continental interior west of the Appalachians. A century later, the United States exercised sovereignty over the core of the North American continent; the enslaved population of what was now the United States had increased from less than four hundred thousand in 1760 to nearly 4 million in 1860; plantation slavery was thriving from Virginia across the vast southern interior that stretched from Georgia to Texas; and the United States had supplanted Europe’s Caribbean colonies as the main source of slave-produced commodities in the Atlantic World. In many ways, the 1860 election pivoted on the question of whether the federal government would use its powers to keep the United States on the “high-road to a slave empire,” as Abraham Lincoln quipped to William Seward. The transformation of the North American continent in the century between the Seven Years’ War and the American Civil War was nothing short of remarkable; slavery and empire stood at the heart of that transformation.¹

How did an independent United States emerge as the dominant power on the North American continent? How did the United States become the Atlantic World’s preeminent empire for slavery? While historians have, of course, addressed these questions, for a long time their answers remained separated by historiographies that removed the United States from the broader history of the Americas and the Atlantic World and then subsumed the history of slavery’s growth and expansion on the North American continent into the inevitable expansion of the United States. Historians then divided the history of the United States into largely distinct colonial, early national, and antebellum and Civil War periods. In turn, they severed the expansion of slavery and empire in colonial North America from that of slavery and the United States after 1776. Likewise, by dividing this history into distinct early national and antebellum phases, historians overlooked the important continuities that connected the expansion of slavery and empire from the 1760s into the 1850s. The fragmentation of American history into narrow, specialized fields such as political and social history similarly narrowed the analyses of historians interested in slavery and expansion. By severing the political history of slavery and expansion from frontier and African American history, historians analyzed the expansion of slavery in the United States as a domestic political matter, determined by internal political factors such as the sectional makeup of major political parties.²

Since the turn of the twenty-first century, however, the historiographies of slavery, politics, and empire have changed profoundly and increasingly overlap in both subject matter and chronological scope. Historians now analyze American slavery as a dynamic, Atlantic, imperial, and continental institution that both underwent profound changes and exhibited important continuities from the colonial period through the Civil War. Slaves and free people of color are treated as political actors who shaped the local, national, and imperial politics of race and slavery. African American history is framed as not just the search for freedom and integration into the mainstream of white American life but also a series of broad, hemispheric struggles for autonomy, self-defense, and self-determination.³ Whereas political historians once divided the politics of slavery in the United States into distinct early national, antebellum, and Civil War eras, they have increasingly joined these periods by focusing on struggles between slaveholders and others over the deployment of state power to protect and promote—or to attack and abolish—slavery. In addition, historians have shown how developments in the Atlantic World continuously shaped the politics and geo-politics of slavery in British North America and then the United States.⁴ Finally, the emergence of the United States as a continental power was once the...