Over the last thirty years, historians and historically minded political scientists have effectively overturned the long-held perception of the nineteenth-century United States as a polity defined by its lack of an effective state. By highlighting the myriad interventions of its energetic and enterprising federal government and by incorporating subnational governments and private actors and organizations as evidence of its impressive “infrastructural” power, a generation of scholars have, collectively, described a nineteenth-century state that was both more assertive and more robust than was previously thought. Yet other scholars have begun to ask whether this interpretation has concocted a state stronger and more coherent in prospect than it was in practice. By highlighting the piecemeal and often partial nature of the nation’s institutional development and the contradictions and incoherence that accompanied its infrastructural power, these scholars have laid the foundations for a new “improvisational synthesis” that stresses the equivocal nature of American state-building and considers its enduring vulnerabilities.