Pulitzer Prize-winning historian Steven Hahn reinterprets the eight decades surrounding the Civil War as a period of continental imperialism rather than simply sectional conflict. The book places slavery, Indian removal, the Mexican-American War, and overseas expansion in a single framework, showing how American expansion involved the simultaneous extension and contestation of slavery, the dispossession of Indigenous peoples, and debates about who counted as American. Hahn challenges periodization that treats the Civil War as a clean break, showing continuities in ideas about race, citizenship, and empire that persisted from the antebellum period through Reconstruction and beyond. He examines how enslaved people and Indigenous nations experienced and resisted American expansion, making them actors in rather than merely objects of history. The book gives attention to the Pacific and Caribbean as well as the familiar story of westward expansion, revealing how continental and overseas imperialism were linked. Hahn writes in accessible prose while advancing sophisticated historical arguments. For readers seeking to understand how race, slavery, and empire shaped American development, this work provides a compelling synthesis that challenges familiar narratives of American history.