This dissertation analyzes how United States naval officers’ beliefs about race and slavery shaped sectionalism between the North and South in the antebellum era. As agents of the federal government operating far from the capital, naval officers had significant influence on the implementation of American foreign policy. With reputations as respected professionals and travelers, they also shaped national discourse with their reports, speeches, and publications. These traits made officers important public figures as the future of slavery became a pervasive issue that increasingly affected American naval operations. The study examines the US Navy’s suppression of the transatlantic slave trade, support for African colonization in Liberia, policing of unauthorized “filibustering” invasions in Latin America, and exploring expeditions. It argues that up until the secession crisis at the outbreak of the Civil War, the naval officer corps was remarkably resilient to the growing divide between the North and South. Most officers considered themselves to be politically moderate on the issue of slavery, and they tried to curtail the institution’s worst excesses, eliminate threats to the stability of slavery, and promote external, compromise solutions to the nation’s domestic crisis that prioritized rule of law. These solutions sought to unify white Americans around visions of empire and the expatriation of African Americans. In pursuing such goals, officers tried to enact their own version of American foreign policy. Though they had limited material success, their efforts supported political moderatism in the antebellum United States. As more and more Americans took up pro- and antislavery stances, naval officers used federal power and their personal influence to help maintain the belief that compromise could preserve the Union.