Abstract This paper develops a new framework for understanding when and how migrants shape culture, applying it to the Confederate diaspora—a small migrant group that left a large cultural imprint. Southern Whites that migrated after the Civil War played a pivotal role in spreading Confederate symbols and racial norms across the U.S. by the early 20th century. Their far-reaching influence stemmed from two key conditions: (i) an ideological intensity rooted in their experiences of slavery, secession, and military defeat and (ii) access to malleable power structures during westward expansion and post-war reconciliation. These conditions enabled them to transmit Confederate culture to both kin and non-Southern neighbours and to expand their reach by mobilising civil society organisation and leveraging positions of authority. They shaped policies and institutions that helped entrench racial norms and inequalities in labour markets, housing, and the criminal justice system. Our findings provide empirical foundations for understanding how migrants can transform local culture, rather than merely assimilate.