This historiographical essay argues that from the 1990s to the 2010s work on nineteenth-century immigration to the United States became increasingly “imperial.” Not only did historians of immigration address US territorial conquest and incursions abroad, but they also examined the disputed and changing boundaries of federal power within the country and proposed that hierarchy and inconsistency were persistent features of governance, not ever-diminishing exceptions to the rule. The essay includes analyses of scholarship on whiteness, transnationalism, borderlands, and the exclusionary laws and practices that especially targeted the Chinese. It concludes that an imperial framework usefully balances the importance of state action against the diversity of local experiences and suggests that work on immigration is useful for conceptualizing the Civil War–era United States as a whole.