How does jus contra bellum apply to States in their Relations with the Self-proclaimed Republics in the Donbass?

The escalation in February 2022 of the conflict between Ukraine and Russia that first began in 2014 has not been the subject of particularly divergent opinions from an international legal perspective. The overwhelming majority of States and authors condemn the Russian military operations as a blatant act of aggression pursued in violation of the United Nations Charter. Yet, it might be useful to examine the reactions prompted by the main argument deployed by Russia as to the right of the Peoples' Republics of Donetsk and Luhansk to benefit from military assistance by virtue of collective self-defence recognized in customary international law and codified in Article 51 of the United Nations Charter. This argument raises the question of the applicability of the jus contra bellum regime to relations between States and secessionist entities which has already been debated. This contribution argues that the war in Ukraine sets a precedent which confirms that self-defence is a justification exclusively available to States and that secession or territorial annexation secured through forceful means cannot be recognized, while addressing how one can understand, from an international legal perspective, that this has sometimes been the case in the past. [ABSTRACT FROM AUTHOR]