This article relates the conduct of the war against Paraguay to the process of state building in Argentina. The research focuses on the rise of the Liberal-Unitarian party and the subsequent plot that brought several provincial leaders into its centralizing sphere. Mobilization for the conflict against Paraguay accelerated the process of centralization, by subordinating provincial leaders more consistently. Such subordination was achieved through a combination of military recruitment and repression against dissident oligarchies. Thus, the campaign against Paraguay was simultaneously an international conflict and a continuation of the long Argentinean civil war. Keywords: Argentina, Unitarians, War of the Triple Alliance, Nationalization.