What is citizenship? Who can be a citizen? What are the rights and duties of a citizen? And who decides the answers to these questions? These are the issues at the heart of the Pulitzer Prize–winning historian Eric Foner’s life’s work, concisely treated in his most recent book, The Second Founding, whose subtitle How the Civil War and Reconstruction Remade the Constitution provides a preview of his answers. As Foner argues, it was the Civil War and the subsequent Reconstruction Amendments to the Constitution that shifted the power to determine these issues from the states to the federal government and, in the process, radically expanded who was entitled to membership in the American political community and the basic rights enjoyed by virtue of that membership. The Thirteenth Amendment (ratified in 1865) abolished slavery; the Fourteenth (1868) guaranteed citizenship and equality for anyone born in the United States; and the Fifteenth (1870) explicitly gave black male citizens the right to vote. Though, as Foner repeatedly laments, these Amendments have yet to fulfill the lofty goal of their congressional drafters—and the political community that supported them—to “build an egalitarian society on the ashes of slavery.” The villains of the story are in equal measure northern racism, southern intransigence, and the federal judiciary.

Before the Civil War, questions about the nature of citizenship were more unsettled than a modern reader might expect. More or less by default, state law largely governed the issue of who was a citizen and