The purpose of the paper is to discuss the emergence and decline of national and / or ethnic minorities in the borderlands around the Baltic Sea. The socio-political development of ethnic groups is seen as a result of different influencing factors: The territorial history, the change of state borders and population groups plus relations beyond the state territory. Several criteria were found to determine the development, non-development or decay of national allegiance. The change, establishment or eradication of state boundaries, the ethnic cleansing of areas, mostly for the sake of “nation-state” homogeneity, the assimilation of a potential ethnic group into the majority population, and the non-emergence of a national movement.