This paper attempts to provide a theoretical basis for the EU crisis on the development of integration in the past decade (2009 to 2019). First, it analyzes neo-functionalist integration theory, and the revision and amendment thereof, with reference to the concepts of new institutionalism and constructivism. Second, three main gaps are apparent in multiple EU crises-between commitment and implementation, between elite and public opinion, and between a European and national identities. Third, arguments are offered on the factors which caused the EU crisis on the basis of the theory of amended neo-functionalism. The final part concludes the EU crisis had its origins in the divergence between interest distribution and identification.