My dissertation addresses two .major shortcomings in the literature on nationalism: the relative absence of causal arguments explaining the transformation, as opposed to the emergence, of nationalism, and the relative lack of comparative studies on nationalism in Latin America. I propose a comparative-historical analysis of why nationalism radically changed in Argentina, Mexico, and Peru during the 1880-1950 period. In the late nineteenth century, all three countries featured highly exclusionary forms of nationalism, which perpetuated the ethnoracial divisions from the colonial period. In the first decades of the twentieth century new models of popular nationalism, which envisioned an homogeneous national identity to "overwrite" colonial divisions, gained state support in Mexico and Argentina. By contrast, in Peru, the old exclusionary nationalism managed to persist. I hypothesize that successful transitions towards more popular forms of nationalism were driven by the conjuncture of a) the emergence of state alliances with subordinate classes, and b) the state's "ideological capacity" to produce and institutionalize new national ideologies. My research design is organized to track empirical manifestations of nationalism in school textbooks, radio broadcasts, intellectual writings, and public rituals by combining secondary sources with primary archival work.