Convergence and Divergence Between International Humanitarian Law and the Law of Neutrality in Inter-State Military Assistance: Lessons from Recent State Practice in the Russia-Ukraine Conflict

With the outbreak of the Russia-Ukraine conflict, the provision of military assistance by Western States to Ukraine has led to the re-emergence of debates on the legitimacy of inter-state military assistance in IACs. Russia's assertion of the legitimacy of its armed response to any form of military assistance highlights the importance of discussing the consequences that States may suffer when engaging in such assistance. This paper attempts to categorise the various forms of support provided by States in IACs in order to examine when they can determine the acquisition of party status and the consequent application of the rules of IHL to the assisting State. This categorisation will be used to assess the consequences of party status for States far from the battlefield, in order to distinguish them from those arising from violations of neutrality law, also in light of the recent practice linked to the Russia-Ukraine conflict. This analysis will be then used to contrast claims that interstate military assistance easily leads to the involvement of the assisting state in armed conflict, exposing it to military reactions. Finally, it examines whether other international rules establish consequences arising from the party status, focusing on those relating to treason and naval warfare, as these have also been the subject of debate during the Russia-Ukraine conflict.