We propose a theory of how collective memories of inter-ethnic war violence can persist along generations and lead to different contingent patterns of voting behavior. Specifically, exposure to violence by one ethnic group generates hostility that over time spills over other ethnic groups; this generalization of inter-group attitudes is encouraged by appeals to national identity against non-nationals. To test our theory, we use a historical case of indiscriminate violence against civilians by French-North African troops in Italy during the last phase of World War II. We find that, in current days, formerly victimized communities reward more political parties that shift towards more nationalist and anti-immigration platform, compared to otherwise similar communities. These results are not driven by pre-war differences in political preferences, or in socio-economic characteristics.