The success of minority nationalisms and their claim to autonomy is primarily dependent on the popular support they receive from their constituencies. Aspirations of minority groups demanding self-rule are also accepted as democratic because of this popular consent. The unsuccessful autonomy referendums in both Puerto Rico and Corsica, however, deviated from this trend leaving questions behind about where and when autonomy is likely to be a democratic and realistic solution. The article elaborates on five variables explaining popular support for ethnonationalism and questions their reliability across the cases of Quebec, Flanders and Western Thrace. Experimenting with the most different systems design (the Mill’s method of agreement), this article concludes that minority nationalism is stronger in political systems of ethnic differentiation than assimilation. The article also verifies this in the contrasting cases of Corsica and Puerto Rico where the nationalist factions failed to mobilize their ethnic constituency because of their political culture being divided by the political systems of integration and assimilation.