Since the end of the Second World War, European states---in sharp contrast to Europe's past and to other world regions---have shown a strong tendency to resolve their irredentist disputes peacefully. Inquiring into the origins of this development, I focus on the evolution of the territorial status quo norm in Europe. I depart from the existing literature on norm selection in three important ways: First, my research inquires in depth not only into the international but also the domestic processes through which nation-states select norms. Second, I elaborate on argumentation theory. I argue that norm selection through persuasive argumentation entails not only constructing a link between the advocated normative idea, the dominant identity and already selected norms, but also building such a link between the normative idea and the dominant episteme. The latter is a lens---similar to a paradigm---through which actors make the world intelligible to themselves. Third, I do not dichotomise rationalist and constructivist selection mechanisms but propose a synthesis. If a number of conditions are present, states select norms in three ideal-typical stages: (1) Environmental change provides the impetus for a new advocacy for a normative idea; (2) advocates persuade large segments of elites and public to select this idea by abstract, comparative, and appropriateness reasoning; (3) recalcitrant actors, seeking to avoid the costs of opposing the newly established majority view are eager to reach a compromise with the advocates. Focusing on the irredentist claims by the Federal Republic of Germany and the Republic of Ireland, this study's empirical research generates evidence for and further elaborates on the three-stage norm selection mechanism but also cautions not to confuse the ideal-typical stages with real-types.