A growing literature examines why and under what conditions citizens are willing to fight for their country, yet it often overlooks societal heterogeneity. In multiethnic states, ethnic minorities may hold fundamentally different views about defending a majority-dominated nation-state. We argue that in divided societies, citizens’ willingness to fight is deeply shaped by cultural identity and historical narratives, which influence threat perceptions and, ultimately, readiness to fight. We test our argument in the crucial case of Latvia, a country with a sizable Russian-speaking minority and heightened security concerns about neighbouring Russia. Using three waves of original survey data (2022–2024) and logistic regression models, we find evidence of a ‘minority effect’: On average, Russian speakers are less willing to fight for Latvia than ethnic Latvians. A mediation analysis shows that this disparity is substantially driven by divergent historical memories. Russian speakers display greater Soviet nostalgia and are less likely to perceive Russia as responsible for the war in Ukraine, which in turn reduces their willingness to fight. Our findings have important implications for defence planning and resilience in multiethnic states facing external threats.