This paper studies the role of compulsory military service in the process of nation- building. We pair original survey data covering 29 cohorts of conscripts in Argentina with random variation in service emerging from a lottery. We find that military ser- vice leads to stronger national identity and better attitudes toward fellow countrymen several decades after serving. We document complementary mechanisms that explain these patterns: First, using natural language processing techniques on open-ended re- sponses, we find suggestive evidence that social integration and national attachment were actively inculcated during service. In line with value transmission, former con- scripts also tend to adopt the ideology of the government under which they served. Second, exposure to diverse peers and developing a more diverse social network rein- force the baseline patterns. We find no evidence that these results materialize through other mechanisms, such as conflict exposure, labor market outcomes, religiosity, or family formation. Taken together, these results show that conscription can effectively contribute to nation-building.