Knowledge about "happiness" means power. For the self-portrayal of a nation, its system of values and morals, knowledge about happiness can be used and reinterpreted as an emotional-political instrument of power. How did knowledge of happiness change after 1933? In the years of crisis and war, which were marked by propaganda, persecution, the Second World War and the Holocaust, knowledge of happiness had a mass psychological function in Nazi Germany within the framework of the racist work moral "Kraft durch Freude" ("Strength through Joy") and in Switzerland in the context of the cultural-nationalist emotional policy of "geistige Landesverteidigung" ("intellectual national defence"). Isabelle Haffter shows the constructedness of happiness knowledge as an ambivalent expert and popular knowledge, which is characterised by change and continuities. The aim of the study is to uncover a research gap in the transnational history of knowledge and emotions about cultural nationalisms by means of historical case studies from the fields of politics, science and the performing arts.