Large-scale infrastructural projects have proven popular with "Third-world" countries in their search for national integration and political stability. My research examines these efforts at state formation and nation-building by analyzing the process of electrification in the Peruvian Andes from the Great Depression through the Cold War, particularly the Mantaro hydroelectric system completed in 1973. During this period, electrification transformed the Andes by expanding the state, altering national conceptions of geography, and adapting western scientific practices to particular topographical contexts. I explore why, despite its technological capacities, the Peruvian state – like others in the Global South – is still seen as "weak" by scholars, and more importantly, its own citizens. Although a technological success, I argue that electrification was based upon contradictory goals: while some intellectuals and statesmen believed that electricity could strengthen inherited colonial structures; others alternatively saw it as a reformist and even revolutionary means to dismantle traditional hierarchies. The electrical grid physically unified large parts of the country, but simultaneously highlighted divisions in Peru's political class, paradoxically underscoring the political weakness of the very state that built it. A country with a long history of implementing infrastructural projects, Peru makes an illuminating site for broader global debates on the connection between infrastructural development and state formation in the Global South. The country's geographic challenges – overcoming the Andean mountain chain and its associated social disparities – transformed under hydro-electrification an "obstacle to development" into a developmental "possibilism." Ultimately, the growing gap in these projects between the state's technological prowess, and its legitimacy with its own citizens, exemplifies a political weakness felt across many Third-world developmental regimes.