The invasion of Ukraine by the Russian Federation represents an extremely serious violation of fundamental norms of International Law: an aggression. None of the justifications invoked by Russia individual or collective self-defense, linked with the pretext of the protection of nationals or humanitarian intervention-is admissible in the light of International Law. But in the context of the renewed reflection on the international order and disorder, it must be noted that serious violations of the United Nations Charter in matters of international peace and security carried out directly or with the sponsorship of one or more of the permanent members of the Security Council have been repeated on several occasions, after the end of the Cold War. Hence, taking into account international practice, the aspiration that after the end of this war there will be a return to the international order according to the letter, and even the spirit, of the Charter is perhaps illusory: the Organization's natures has changed and (many of) its Member States have changed their conception of the commitment, responsibilities and obligations that multilateralism brings with it.