The EU legal system, with its many hands and complex architecture, in which national and European powers are closely interwoven, requires a particular form of cooperation. This delicately developed cooperation may be influenced by the EU's ambition to take a statelike role in international relations. Indeed, the basic assumption underlying this Article is that it is not only the EU's complexity that influences the EU's external actions—usually seen as limiting the EU's capacity to speak with one voice—but also that the EU's external actions influence its internal set-up and cooperation practices. As a result of the EU's participation in international legal regimes, established organizational principles might come under pressure. Furthermore, within the complexity of the European legal order, the potential consequences could be more disturbing for stability than within the—monolithic, in comparison—structure of states.