The federal principle stands for duplex regimen—the existence of two governments within a compound polity. It represents an architectural principle which attempts to find ‘unity in diversity’. To protect the autonomy of each government, powers are divided between the centre and the periphery. In federations, there are then two governments that could potentially engage in foreign affairs. Yet, despite the internal division of power, classic international law responded to the emergence of federal States ‘by ignoring their constitutional characteristics and assimilating them to other sovereign States’. The federal principle would here be reduced to an internal phenomenon that would structure the constitutional relations between the two governments. Not all federal States would adopt the classic international law solution and distinguish between a federal ‘internal’ and a unitary ‘external’ sphere. The solutions adopted by federations have varied in time and place. Each of them had to answer a series of constitutional questions. Should the federal Union be constitutionally entitled to conclude treaties that fall into the exclusive competences of its member states? Could the member states of a federation themselves conclude international treaties? What constitutional mechanisms would best preserve unity within the diversity for foreign affairs?
Robert Schütze is Professor of European Law and Director of the Durham European Law Institute. In the past, he has been a Visiting Professor or Fellow at the British Institute of International and Comparative Law (London), the Centre for European Legal Studies (Cambridge), Fribourg University (Switzerland), the Institute of European and Comparative Law (Oxford), and the Max-Planck Institute for Comparative Public Law and International Law(Heidelberg). He has also been a Fulbright-Schuman Scholar at the Centre for European Studies at Harvard University. He also co-directs the Global Policy Institute; and he is also a Visiting Professor at the School of Government of LUISS Guido Carli University (Rome).