Between 1815 and 1861, American constitutional law and politics underwent a profound transformation. These decades of the Interbellum Constitution were a foundational period of both constitutional crisis and creativity.   The Interbellum Constitution was a set of widely shared legal and political principles, combined with a thoroughgoing commitment to investing those principles with meaning through debate. Each of these shared principles—commerce, concurrent power, and jurisdictional multiplicity—concerned what we now call “federalism,” meaning that they pertain to the relationships among multiple levels of government with varying degrees of autonomy. Alison L. LaCroix argues, however, that there existed many more in the early nineteenth century than today’s constitutional debates admit.   As LaCroix shows, this was a period of intense rethinking of the very basis of the U.S. national model—a problem debated everywhere, from newspapers and statehouses to local pubs and pulpits, ultimately leading both to civil war and to a new, more unified constitutional vision. This book is the first that synthesizes the legal, political, and social history of the early nineteenth century to show how deeply these constitutional questions dominated the discourse of the time.