摘要 : Regional Organizations (ROs) have become a central pillar of governance beyond the nation-state. This paper investigates why European states turned into architects of regional regime complexity: they have created and joined numero... 展开 Regional Organizations (ROs) have become a central pillar of governance beyond the nation-state. This paper investigates why European states turned into architects of regional regime complexity: they have created and joined numerous different ROs and equipped them with a broad range of different policy competencies. Thereby, European states - some more than others - have increasingly duplicated identical policy competencies in multiple ROs. The phenomenon is puzzling as it is potentially costly and might undermine the effectiveness of regional cooperation especially if incompatible regional rules trigger non-compliance. Therefore, we ask why states differ in the extent to which they cover identical competencies in different ROs. Drawing on a unique dataset and analyzing cross-sectional temporal variation, we show that both indirect factors, such as late accessions and the number of states in Europe, as well as direct factors, such as state power and democracy, drive regional regime complexity. 收起