Regional integration theory seeks to explain the establishment and development of regional international organizations. Key questions are why and under which conditions states decide to transfer political authority to regional organizations; how regional organizations expand their tasks, competencies, and members; and what impact they have on states and societies in their regions. The main (families of) theories explaining the development of European integration—rather than decision making and policy-making in the EU—are intergovernmentalism, neofunctionalism, and postfunctionalism. Regional integration theories have closely followed and adapted themselves to the development of European integration. They cover the establishment and progress of supranational policies and institutions but also the recent crisis of the EU. An exemplary review of their explanations of major development in European integration shows that they are more complementary than competing.
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