European states have a long history of banking sector nationalism. Control over credit allocation is believed to contribute to economic development and competitiveness goals, insulation from external economic shocks, and control over monetary policy. This paper explains the potentially dramatic loss in domestic control over banks created by the European Banking Union (EBU). First, we argue that ongoing liberalization in the global and European economies has made banking sector protectionism both more costly and conflictual. Second, we contend that because many of the biggest banks have internationalized their operations, they now prefer centralized European regulation and supervision. Third, supporting a modified neofunctionalist argument, we find that behind the sometimes frenetic intergovernmental bargaining in 2012-14, it is primarily the European Commission and the European Central Bank that have pushed Banking Union ahead. Supranational institutions have argued, with some success, that they have unique capacity to solve collective action and prisoners’ dilemma problems. Contrary to accepted wisdom, Germany has not set or limited the Banking Union agenda to a great extent, in part because of its own internal divisions. Moreover, the Commission and the ECB have managed at critical junctures to isolate Germany to secure the country’s assent to controversial measures.