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

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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.

Reconciling new Charter interpretations with the customary prohibition

For a use of force authorised through Uniting for Peace under a new interpretation of the Charter not to be in violation of the customary prohibition, it seems one of the following would need to be true:

1) the Article 31(3)(b) subsequent practice establishing agreement to interpret the Charter in this way also fulfils the requirements of State practice and opinio juris to simultaneously modify the customary prohibition of force so as to expand the limits of the collective security exception (or narrow the prohibition; but that probably amounts to the same thing) so that force authorised in this way is no longer prohibited by custom; or

2) no change to customary international law is necessary. In the same way that, as Dapo argues, the reference to the ‘inherent right’ of self-defence in Article 51 is ambulatory (its content changes automatically to mirror changes in customary law) and the content of that exception to 2(4) changes as the customary law on self-defence changes without requiring modification of the treaty provision, the collective security exception to the customary prohibition is also ambulatory. The exception to the customary prohibition is not ‘force authorised by the UNSC under Ch VII’ but ‘force lawful under the Charter’, whatever that is interpreted by UN Members to be at a particular time, and the content of the exception will track the changes in the treaty law.

On balance, option (2) seems more plausible. It is by no means clear that subsequent practice under Article 31(3)(b) would necessarily also be sufficient to meet the requirements of State practice and opinio juris to change customary law. Moreover, assuming both the customary and jus cogens prohibitions prohibit any force that does not fall within either of the two established exceptions, with option (1) you are not only modifying the customary prohibition on force but would also be modifying the jus cogens norm by changing the prohibition/exception boundary. Unless both the test for modification of custom and that for modification of a jus cogens norm were met simultaneously, the change in custom would not be effective since no rule of custom can come into existence if it comes into conflict with a jus cogens norm (see Conclusion 14, ILC Draft Conclusions on Peremptory Norms of General International Law (Jus Cogens)). Although the test for modification of jus cogens is a high threshold to meet, it is certainly not impossible – jus cogens norms may be modified by another norm of the same character (Article 53, VCLT). Moreover, a unanimous, consensus or even ‘very large majority’ vote of the General Assembly seems rather attractive as a means for the ‘international community as a whole’ to evidence its recognition of a new or modified jus cogens norm.

Whether option (2) will work depends on how broad the ambulatory collective security exception to the customary prohibition is established to be. Does the exception exclude ‘force authorised under the Charter’, ‘force authorised by the Security Council’ or something else? It seems that, as the rules relating to authorisation of force by the UNSC have changed since adoption of the Charter – for example, through interpretation of Article 27(3) UNC by subsequent practice to allow force authorised by decisions adopted with the abstention of a permanent member – the kinds of force excepted from the customary (and jus cogens) prohibitions have expanded in parallel. However, depending on how broad the exception is, it could be the case that using Uniting for Peace in this way would be such a significant change to the collective security arrangements under the Charter that it would go beyond just a change in the ambulatory content of the collective security exception and require a change to the outer limits of the exception. That is, at what point would option (2) turn into option (1), engaging the exception/prohibition boundary, and modifying the customary and jus cogens prohibitions? The answer to this question about the limits of the collective security exception would have to be found in the reactions of States to any effort to interpret the Charter in this manner – would mere subsequent practice among UN members be accepted as sufficient to make force authorised through Uniting for Peace lawful, or would States also push to see the ‘international community as a whole’ recognise the new contours of the jus cogens prohibition on force?

Authorisations of force outside the Charter system?

Pushing this line of thought even further, Article 4(h) of the Constitutive Act of the African Union recognises ‘the right of the Union to intervene in a Member State pursuant to a decision of the Assembly in respect of grave circumstances, namely: war crimes, genocide and crimes against humanity.’ On one view, force used under this provision would simply not be covered by either the customary prohibition or Article 2(4). On this view, African Union States have consented to any such uses of force against them through their ratification of the Constitutive Act. However, the correctness of this argument depends on whether the possibility for a State to render uses of force against it lawful by consent applies not only to cases of consent to a specific use of force, but also to a general prior consent to force to be used at an unspecified time (or times).

If the prior consent of AU States through the treaty is not able to render the force authorised under 4(h) lawful, any force used by AU States against another State pursuant to such a decision of the AU Assembly would violate the customary prohibition on force. In addition, even assuming the Constitutive Act would not already be void under Article 53 VCLT for being in conflict with the jus cogens prohibition on force (which doesn’t appear to be the case based on the reactions of States), any authorisation of force by the AU alone under this provision would also appear to violate Chapter VIII of the Charter. In particular Article 53 provides that ‘no enforcement action shall be taken under regional arrangements or by regional agencies without the authorization of the Security Council.’

If UN members can interpret the Charter through subsequent practice so that force authorised by the General Assembly no longer violates Article 2(4), could they also interpret it so that enforcement action authorised by certain regional arrangements without UNSC authorisation would not violate 2(4) either? However, unlike the proposed Uniting for Peace interpretation, this would require an interpretation directly contrary to the existing text of the Charter, in this case Article 53. While Article 31(3)(b) VCLT does not explicitly impose any limits to the interpretations possible under that provision, subsequent practice under 31(3)(b) is only to be ‘taken into account’ alongside the elements for treaty interpretation in Article 31(1), including the ordinary meaning of the treaty terms. This could prevent such a radical counter-textual interpretation of Article 53 through practice, and require UN Members to instead go through the Charter amendment procedure.

Even if such an interpretation of the Charter were possible, the same question then arises as for the Uniting for Peace interpretation, but more acutely. By giving the power to authorise force to a body outside the Charter system, would this interpretation be such a significant expansion of the collective security exception that it would go beyond what was possible through an ‘ambulatory’ understanding of the exception, and oblige States to satisfy the requirements for modification of both the customary and jus cogens prohibitions on force?

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Kevin Jon Heller says

November 26, 2019


This is a great post -- and I'm particularly happy to see you acknowledge that Art. 4(h) of the Constitutive Act is based on state consent. (Per the recent workshop, many scholars try to invoke it as support for unilateral humanitarian intervention.)

I have never quite understood, however, what the legal objection would be to AU states granting prior general consent to force being used on their territory, as opposed to contemporaneous consent to a specific use of force. What principle of international law would permit the latter but prohibit the former?

I'm not saying you accept the difference. Just curious if you have an answer -- I've read most of the scholarship on Art. 4(h) and am still looking for one!

John R Morss says

November 27, 2019

Thanks Katie for the very interesting and timely post.
As you helpfully raise and as KJ points to, surely prior consent to cross border use of force (aka invasion) includes conditional consent as in 4(h). (Indeed any such consent, however orthodoxly contemporaneous, surely includes implied conditions?)
I am more surprised by the suggestion that GA might determine what is and what is not (or is no longer) a jus cogens norm.That seems utopian or even panglossian... one doesn't have to be a bolted-on positivist on the "Sources" to demur. NB such a mechanism would seem to be an extreme opposite (and in its own way positivist?) speculation to the proposal from Dapo that 'evolving' CIL continually updates the content of Charter on use of force: his point on proportionality and necessity being thus contributed is a very important, perhaps even a decisive one, ... yet we surely fetishize CIL (a la ICRC at times?) if its role is so exhalted. The ad hoc shadow finding in Nicaragua surely does not support such a status as driver of norms, for if that is correct why do we have the Charter at all?

Rana Moustafa says

November 28, 2019

Thank you Katie for your very interesting post. However, I respectfully disagree with your starting point that there is a peremptory norm that prohibits the use of force except in the case of self-defense or in case of an authorization by the Security Council. I believe that the jus cogent prohibition on the use of force concerns only the use of force outside the UN system given that the object of this norm is "to replace a rationale of a unilateral use of force by mechanisms instigating collective security" (Olivier Corten, The Law Against War, p.500). A contrario, the use of force on the basis of an authorization from the UN, regardless of the authorizing organ, is not prohibted by the peremptory norm of the prohibtion of force. Accordingly, the legality of the uniting for peace resolution does not require any change to the jus cogent norm of the prohibition of force.

Sachintha Dias says

November 29, 2019


Thanks for this incisive post. I have a broader query re your second proposition - that the collective security exception to the CIL prohibition of the use of force is ambulatory. Assuming the whole of the CIL prohibition to be jus cogens, I find it difficult to conceive of a jus cogens rule that is contingent on the evolving interpretation of the text of a treaty.

In my mind, the different options for reconciling the Charter with the CIL prohibition when the Charter came into force are: (i) the Charter incorporated the content of the existing CIL prohibition of the use of force, including some sort of collective security exception in the CIL rule which the Charter procedurally regularised (ii) the CIL prohibition when the Charter came into force was not jus cogens (iii)the content of what was to become Article 53 VCLT was not yet CIL (iv) the Charter modified the existing Jus Cogens rule in accordance with the content of what was to become Article 53. I wonder what your view is and whether it has an impact on how broadly you can construe the collective security exception in the CIL prohibition. Thank you!

Katie Johnston says

November 29, 2019

Dear Kevin, John and Rana,

Thank you all very much for your comments.

On 4(h):
Consent does seem like the more promising argument in favour of the legality of 4(h) as, for the reasons Dapo sets out, relying on a customary right of HI emerging seems problematic. I agree that it is hard to identify a specific legal rule that would prohibit such an open-ended consent being given. Open-ended prior consents exist elsewhere in international law, for example in the v different context of consent to ICJ jurisdiction (thanks to Ulf Linderfalk for this example), but there doesn’t seem to be any prior practice of this kind of consent-based collective security mechanism - of course, this wouldn’t necessarily prevent one emerging. As I argue above, I think UNSC authorisation is ‘built in’ to the customary and jus cogens prohibitions and does not operate through consent. The customary and jus cogens prohibitions grew out of (or were at least significantly shaped by) Art 2(4), a provision in the same treaty that establishes the UNSC. 4(h), arising long after the conventional, customary and jus cogens prohibitions became established, does not enjoy the same special position outside the prohibition, and another legal basis for any such uses of force will need to be found.
This kind of prior treaty-based consent also raises interesting issues around withdrawal of consent. Presumably as soon as there was any chance of 4(h) being invoked against an AU Member there is a risk of that Member withdrawing from the treaty. The AU constitutive Act contains a one year delay from notification of cessation of membership to it taking effect during which the Member has to continue to abide by its obligations (Art 31). The interesting question is whether it is possible for the withdrawal of consent to the use of force to be conditioned in this way – although as you say there is no obvious rule of law preventing this.

On the GA and jus cogens:
As I understand it, a jus cogens norm comes into existence when an existing norm from one of the sources of international law (in my view this can only be custom, but there are a range of opinions) is recognised by the international community as a whole as being a norm from which no derogation is permitted. That is, a special, additional form of opinio juris is required to transform the regular customary norm into a norm with jus cogens status, which must be manifested by a ‘very large majority’ of States. Of course, (as in Nicaragua when considering GA resolutions as opinio juris for custom) all will depend on the wording of the GA resolution and whether it can be interpreted as evidencing this special opinio juris, as well as the voting pattern of GA Members.

On the scope of the jus cogens norm:
Dear Rana, if I understand your comment correctly I think we might be in agreement. What you suggest about the jus cogens norm prohibiting force outside the Charter sounds similar to what I suggest as option 2. The difficulty is in understanding what is meant by ‘mechanisms instigating collective security’, and if any change to what falls under this concept (e.g. to include the GA as well as the SC) amounts to a modification to the jus cogens and customary norms.

Finally, my thanks to Dapo Akande, Sachintha Dias and Pierre Durand for their comments on earlier drafts of the post.