This chapter explores a hardy perennial – the meaning of the American Civil War – from the standpoints of the nineteenth, twentieth, and twenty-first centuries. It evaluates historian David Potter’s 1968 assertion that, from an international perspective, the defeat of the American South’s bid for independent nationhood and the emancipation of enslaved Blacks, the American Civil War resulted in an unprecedented marriage of liberalism and nationalism, a union unique in the formation of nineteenth-century nation-states. This marriage not only gave liberalism a strength it might otherwise have lacked but also lent nationalism a democratic legitimacy that it may not otherwise have deserved. It also explores how the end of the Cold War and the emergence of multiple decentralizing technologies (cell phones, social media, the internet, etc.) and other polarizing forces which have raised serious questions about whether a more than 150-year-old marriage can survive the centrifugal temptations of the new century.