The last phases and immediate aftermath of World War One represented both the peak of the nationality question and the definitive breakthrough of the minority one. The “morphing” of one into the other (as Holly Case has defined it) is often mentioned in the historiography but rarely analyzed in detail. This article focuses on the key period 1916–1923 and tracks this transition examining the work of different organizations and actors that contributed to it. The article shows that the switch from nationalities to minorities was not absolute. Although the grammar of minorities and majorities was dominant in the interwar years, the vocabulary of nationalities did not disappear and many actors used these terms as synonyms to refer to the same underlying “problem”: the persistence of national difference in an increasingly homogenizing world. Above all, the move from nationalities to minorities foreclosed any possibility of obtaining independent statehood in the new Europe of nation-states. Finally, the article dissects the process whereby the imposition of minority treaties only to Central and Eastern European countries entrenched a stereotypical distinction between a civilized homogenous West and a repressive heterogeneous East that established an understanding of the two areas as undifferentiated monolithic entities.