The need for internal trade and the dangers of external threats have helped hold America together. Disparate factions throughout the country rallied to counter British aggression in the eighteenth and nineteenth centuries; the Germans and the Japanese, in the twentieth; and Al Qaeda, after the 9/11 attacks, in the twenty-first. But, now, without outside threats, the nation is increasingly turning on itself. “We are definitely not united,” Blight said. “Are we on the brink of secession of some kind? No, not in a sectional sense. But, in the interior of our minds and our communities, we are already in a period of slow-evolving secession” in ways that are deeper than ideology and political beliefs. “We are tribes with at least two or more sources of information, facts, narratives, and stories we live in.” The United States today, Blight said, is a “house divided about what holds the house up.”

In his new book, Kreitner argues that, with its politics irrevocably broken, America is running out of time. The potential for physical and political separation is now real, even though the polarization of America does not have neat geographic borders. No red state is entirely red; no blue state is entirely blue. “The twenty-first century has seen an unmistakable resurgence of the idea of leaving or breaking up the United States—a kaleidoscopic array of separatist movements shaped by the conflicts and divisions of the past but manifested in new and potentially destabilizing ways,” he writes. Unlike in the past, the current separatist impulses have emerged in multiple places at the same time. “Often dismissed as unserious or quixotic, a throwback to the Confederacy, the new secessionism reveals divisions in American life possibly no less intractable than the ones that led to the first Civil War,” Kreitner warns.

In the years to come, the appeal of pulling the plug on the American experiment is likely to grow, even among faithful adherents to the idea of federal power. And, if the Union dissolves again, Kreitner writes, it will not be along a clean line but “everywhere and all at once.”