Understanding reparation in cases of shared responsibility of States for internationally wrongful acts : are specific and explicit rules required ?

Public international law regulates interstate relations which, just as human relations, are not always perfect. It is essential to ensure cooperation and coexistence between States, in a world that has become so globalized and where States have become so interdependent. As in any relation, it happens that obligations are breached in the international field. In 2001, the Articles on Responsibility of States for Internationally Wrongful Acts, codified by the International Law Commission, were adopted. Their title is clear: they organize the responsibility of States. Moreover, they provide for rules on reparation. These rules have been used and worked well for decades. However, they are lacking something; they do not regulate (almost) at all cases of shared responsibility, the concept that covers situations where several States have all contributed to a single harmful outcome, each one of them being responsible for their own contribution. Today, it cannot be denied that such scenarios do exist. They are very complex, yet not regulated by international law. Reparation can thus not be granted on a legal basis when shared responsibility is concerned. In this thesis, we explain what that concept is about and how reparation can function when it happens. We answer to the following question: should there be explicit rules in the matter ? We notably have regard to the principle of legal certainty and invoke Justice in general.