This dissertation traces the Jesuit missions' collapse and the Guaraní inhabitants' integration into the Viceroyalty of Rio de la Plata. I argue that globalization and modernization trends—set in motion by Spain's eighteenth century efforts to reinvigorate its crumbling empire—doomed the missions to failure irrespective of the Jesuit expulsion. On the one hand, foreign trade expansion, regional economic growth, and political reforms intensified competition over mission resources and created new opportunities for the Guaraní outside of the missions. On the other hand, the Crown's efforts to exert control over the missions and advance the Guaraníes' temporal well-being worsened living conditions inside the missions. As a result, the Guaraní disengaged from the missions' communal structure or fled the missions altogether. This trajectory reveals the effects of sudden exposure to new cultural values, a largely foreign way of life, and the market economy on a previously sheltered people.

The dissertation interweaves information gleaned from detailed accounting records for thirty missions over more than forty-five years, Guaraní letters, and Spanish correspondence. Integrating quantitative and qualitative sources exposes the underlying causes of the missions' collapse, charts the process of their decline, and brings to light rich details about the lives of a largely illiterate sector of society who did not leave many written records. The result is a rigorous social and economic history that exposes how an isolated region and people became increasingly integrated economically, socially and culturally into the broader Atlantic world over the late eighteenth century.