The process of European integration has been studied and analysed at great length in a variety of academic disciplines. The main focus of this endeavour is usually to try to explain institution-building, policy integration or policy outputs at the European level. In the main theories of integration, domestic politics is a central explanatory factor of the integration process. For example, in the early 'neo-functionalist' theory of Ernst Haas and his followers, one of the driving forces of the delegation of policy functions to the European level was the battle between domestic interest groups, political parties and rival groups of elites. In the contemporary 'liberalintergovernmental' approach of Andrew Moravcsik, the integration process is driven by competition and bargaining between the European nationstates, but 'national' preferences emerge from the on-going processes of domestic politics, where rival interests compete for control of the policy agenda.