Nineteenth-century Paraguay was a provincial backwater of the shattered Spanish colonial empire, a country that had forged its independence under the rule of autocrats, a country where most people spoke Guaraní, a vernacular of indigenous origins. From 1864 to 1870, Paraguay went to war with the Triple Alliance of Brazil, Argentina, and Uruguay. The conflict left Paraguay occupied by foreign armies and devastated with over half its population lost. This dissertation explores a history of state formation, religion, and war in the country before and during this catastrophic time. In particular, the dissertation reflects on how colonial religion helped to produce formative experiences of modern nationhood and citizenship. Conventional interpretations of Latin American history still generally regard the consolidation of nation-states as a starkly secular development. This study questions that formulation and considers how clergy and institutional practices of the Church actually articulated early expressions of nationhood. The dissertation follows how years before the conflict the ruling autocratic regime in the country revived the provincial church and its traditional moral order as recovered vestiges of Spanish imperial sovereignty and reassembled them within a framework of postcolonial republican rule. The sort of pious submission once demanded of royal subjects increasingly defined the rights and duties of republican citizenship. Divine-right mandates and popular sovereignty merged as the ideological foundation of political authority. Moreover fulfilling the sacred obligations of the patriarchal family surged as the primary manifestation of civic virtue. The conflation of values old and new made modern ideas of the republic profoundly, and often painfully, familiar in the everyday lives of Paraguayans. This dissertation thus contends that postcolonial Paraguayans--mostly illiterate, Guaraní-speaking peasants--confronted in their lives a peculiar strain of republican nationalism steeped in religion and articulated in their own language. And, it argues, this engagement pushed them to struggle to extraordinary lengths during the war. The sources utilized range from sermons and local government correspondence, to judicial records of ecclesiastical divorce and suicide, as well as Guaraní-language propaganda produced by the state during the war.