Private international law put to the test of European federalism.

Summary The claim by the European Union, since the end of the 20th century, to have competence in matters of private international law, invites questions about the extent of such competence and its articulation with that of the Member States in the matter in question. The treatment of such a question leads, however, to another, more general question, relating to the point of knowing, when States decide to form a Union of States with an integrative vocation, which entity is responsible for organizing the management of the confrontation of the relations of private interests with the plurality of legal orders, both at the inter-State and international levels. This question, which is recurrent in the United States of America, has now spread to the European Union and can be considered from the perspective of federalism. The impact of federalism on private international law, which it puts to the test, obliges us to modify our understanding of conflict of laws. The function of allocating powers that was previously attributed to it resurfaces, without, however, displacing the function of regulating private interests. The logic of the conflict of laws is turned upside down and leads to the identification of a new category of conflicts, no longer horizontal or vertical but diagonal. These new cases of conflict are multi-faceted and raise questions of the distribution of competences or of the articulation of these competences, and call for a settlement either within the hierarchy or by means of special connections.