This article focuses on the nexus between state infrastructural power and legitimacy. A comparative case study of nationalism in mid-twentieth-century Mexico and Argentina provides the basis for theorizing the impact of state infrastructural power on transformations of official understandings of nationhood. Both countries experienced a transition from liberal to popular nationalism. The extent to which popular nationalism became a regular product of state organizations varied between the two cases, depending on the timing of state development. The temporal congruence between the expansion of state infrastructural power and ideological change, as exemplified by Mexico under Cárdenas, facilitated the full institutionalization of the new official ideology, whereas a disjuncture between state development and ideological change, as exemplified by Argentina under Perón, inhibited such a comprehensive transformation of nationalism.