Il trasferimento di armamenti dall’Unione europea all’Ucraina aggredita: quale fondamento nel diritto internazionale?

The European Union’s decision to support Ukraine, victim of a direct and large-scale aggression started by the Russian Federation in February 2022, has prompted the strong reaction of the Russian gov- ernment. In particular, since the early days of the conflict and to pre- sent days, the Russian Federation has been arguing that the Euro- pean Union’s conduct is unlawful and engenders its international re- sponsibility. The present study aims at evaluating this assertion. This paper investigates the possibility of grounding the European Union’s conduct of assisting Ukraine on a legal basis established by interna- tional law. Strikingly, the analysis allows the identification of two le- gal bases. The first one is the legal regime of collective self-defense, according to which, under certain conditions, it would be lawful to act in self-defense, upon request, together with the attacked State. The second legal basis is the obligation to cooperate to put an end to a serious breach of a peremptory norm of international law, accord- ing to which all States and all international organizations must take action, by means of lawful measures, to put the serious breach to an end. Undisputedly, the breach of the prohibition of the use of force falls within the scope of this obligation.