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Reconciling new interpretations of the UN Charter with the customary international law on the use of force

Published on November 26, 2019        Author: 


In a recent lecture, published as a post on this blog, Professor Dapo Akande analysed the diversity of the rules on the use of force in international law and the implications for the evolution of the law in this area. In this post I wish to address one issue arising from this discussion but not directly addressed in Dapo’s lecture: the impact of changes to the UN Charter on the customary international law rules on the use of force.

In his lecture, Dapo argues persuasively that there are structural difficulties surrounding the evolution of Charter rules, and that these could be avoided if UN members were to interpret the UN Charter through subsequent practice under Article 31(3)(b) VCLT so that a ‘Uniting for Peace’ resolution of the UN General Assembly ‘would be deemed not to be a breach of the prohibition of force under Art. 2(4) in the same way that a Council resolution authorizing force would have that effect.’ However, while this route would avoid the obstacles Dapo discusses that make it difficult to imagine customary international law bringing about a change in the Charter rules on the use of force, it raises the opposite question: how would modification of the Charter rules impact the customary prohibition on force?

As clarified by the ICJ in Nicaragua (Merits, para 179), customary law continues to exist and apply separately alongside even identical treaty provisions. Since the customary and treaty prohibitions exist independently, even if the Charter were to be interpreted so that force authorised through Uniting for Peace was no longer considered a breach of Article 2(4), this interpretation of the Charter wouldn’t automatically change custom to match. A priori, force lawfully authorised by the General Assembly under the Charter would therefore still be in violation of the customary prohibition on force. One could argue that the new treaty rule would simply prevail over the customary prohibition to the extent they conflict, but this seems difficult when the customary prohibition is probably also a jus cogens norm. Indeed, it seems rather that the purported interpretation of the Charter would – by analogy with a new treaty amendment conflicting with jus cogens which would presumably be caught by Article 53 VCLT – be invalid. Read the rest of this entry…