If this was a problem in the previous two centuries, it certainly has not been alleviated in the world in this one:
94. A special instance of this clash of interests is furnished by that political trend (which since the nineteenth century has become widespread throughout the world and has gained in strength) as a result of which (people) of similar ethnic background are anxious for political autonomy and unification into a single nation. For many reasons this cannot always be effected, and consequently minority peoples are often obliged to live within the territories of a nation of a different ethnic origin. This situation gives rise to serious problems.
This problem is not unknown in Europe. “Serious,” in some cases, may be an understatement.
95. It is quite clear that any attempt to check the vitality and growth of these ethnic minorities is a flagrant violation of justice; the more so if such perverse efforts are aimed at their very extinction.
One would expect the Church to condemn ethnic cleansing, given the Nazi and Soviet policies of the 20th century, and the American problem of the 19th.
96. Indeed, the best interests of justice are served by those public authorities who do all they can to improve the human conditions of the members of these minority groups, especially in what concerns their language, culture, ancient traditions, and their economic activity and enterprise. (Cf. Pius XII’s broadcast message, Christmas 1941, AAS 34 (1942) 10-21)
Believers should be deeply inclined to support such minorities in these ways: noting and calling attention to inequities, and advocating along with them for respect, recognition, and self-determination.