One of the most important determinants of the European Union’s role in international affairs is the community’ own definition of the border between states eligible for membership and states that are not eligible. Contrary to what one hears in official pronouncements, this definition has been repeatedly contested and changed significantly since the founding of the community. Prior research (Thomas 2017) has established that contestation from domestic and supranational forces within the community has changed the normative definition of the limits of Europe three times since the 1950s. This paper introduces a new database of all fifty EU decisions on membership eligibility of aspirant states from 1957 through 2017, some positive, some negative, and some reversing an earlier decision. It then uses three analytical techniques – cross-tabulation, regression, and qualitative comparative analysis (QCA) -- to evaluate the relative contribution of these changing membership norms, as compared to other legal, political and economic factors, to the EU decision-making in these fifty cases. All three methods indicate that membership norms exert a powerful effect on EU decisions that cannot be attributed to other factors. The Institutions of Politics; Design, Workings, and implications ( do not use, ended 1-1-2020
