The external action of local communities seems a priori in dichotomy with the sovereignty of the state. Decentralized local authorities are increasingly present internationally through the mechanics of decentralized cooperation. Their actions, although circumscribed by domestic law, can sometimes seem to contradict the major principles of state sovereignty, which at least legally remains the only subject of international law with the related prerogatives, and the actor principal of international relations. From then on weighs the suspicion of a growing collusion between these old and new actors of international relations.