Social facts and policies can be understood only in light of our own perceptions. This holds true with a vengeance where ethnicity, nationhood, or nationalism are concerned. All through the twentieth century this syndromecum-terminological chain has played an extensive, puzzling and usually unpredicted part in structuring social life and political action. New ethnic identities (for example, Tanzania'ism or Indonesian'ism) with their related designations and loyalties have cometo the fore with a speed that reveals the transitional and relational nature of ethnic phenomena. The same holds true for the ups and downs of acute nationalism. On the other hand, many throughout the world would agree with the great Catalonian historian, Pierre Vilar, whose internationalist values are not in doubt, that “in the relationship between my own life and history, nationals problems seem to overwhelm all others.” However one may conceptualize ethnicity and nationalism, their political impact has provided a major and continuous dimension of social action.