Marco Roscini is Reader in international law at the University of Westminster School of Law.

On 24 April, the Marshall Islands filed individual applications before the International Court of Justice (ICJ) against the five nuclear weapon states under the Treaty on the Non-proliferation of Nuclear Weapons (NPT) (United States, United Kingdom, France, Russian Federation, China) and the de facto nuclear weapon states not parties to the NPT (Israel, India, Pakistan, North Korea) claiming a violation of Article VI of the treaty and of its customary counterpart. The Marshall Islands also filed a complaint on the same grounds against the United States and various US organs before a US Federal District Court. While the ICJ has had already the opportunity in the past to address nuclear weapons and nuclear tests, this is the first case specifically dealing with a violation of the NPT. It is not surprising that it is the Marshall Islands that took the initiative: the island state was the location of 67 US atmospheric nuclear tests conducted by the United States from 1946 to 1958. The timing is also meaningful: the applications have been filed after the second Conference on the Humanitarian Impact of Nuclear Weapons in Mexico and just before the NPT Preparatory Committee sessions that will usher to the 2015 Review Conference. The not-so-hidden purpose is to bring back nuclear disarmament to the negotiating table in addition to non-proliferation.

It is of course not possible to discuss here all the issues raised by the applications. I will therefore limit myself to highlight certain points.

First, it is unlikely that the ICJ will have jurisdiction over many of the submitted cases: the NPT does not contain a compromissory clause and the only respondent states that have accepted the compulsory jurisdiction of the ICJ through declarations under Article 36(2) of the ICJ Statute are the United Kingdom, India and Pakistan. While the UK declaration is relatively broad, those of India and Pakistan contain numerous exemptions. In all three cases, the ICJ will have first to determine whether the dispute in question falls within one of those excluded in the declarations. So far, the Court has registered and listed on its website only the cases against UK, India and Pakistan but not those against the states which are reliant on forum prorogatum for jurisdiction.

As to the merits, the main issues are two: how to assess compliance with Article VI of the NPT by the NPT states parties and, with respect to the nuclear weapon states not parties to the NPT, also whether Article VI reflects customary international law.

As to the former aspect, Article VI of the NPT requires all states parties to pursue negotiations in good faith on ‘effective’ measures in relation to: 1) the cessation of the nuclear arms race at an early date; 2) nuclear disarmament; and 3) a treaty on general and complete disarmament under strict and effective international control. According to the ICJ’s 1996 Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, however, Article VI entails not only an obligation to negotiate, but also ‘an obligation to achieve a precise result – nuclear disarmament in all its aspects – by adopting a particular course of conduct, namely, the pursuit of negotiations on the matter in good faith’ (para. 99). General and complete nuclear disarmament is of course a result that is beyond the power of any individual state and an obligation to achieve such result would hardly have any real binding character. As to the obligation to negotiate in good faith, the problem with pursuing individual actions against the nuclear weapon states (not all of which will be subject to jurisdiction) when the breach is in fact a collective one is that each defendant may easily claim that failure to comply depends on the obstructive attitude of the others. Having said that, it should be recalled that, at the 2000 NPT Review Conference, the NPT states parties agreed on a series of 13 practical steps for the implementation of Article VI. It has been suggested that the NPT Review Conferences’ Final Documents may constitute ‘subsequent agreement[s] between the parties’ for interpretation purposes under Article 31(3) of the 1969 Vienna Convention on the Law of Treaties. If this is correct, whether or not the NPT states parties have complied with Article VI could be tested against these steps, in which case it can hardly be denied that the nuclear weapon states have not done much, if anything at all, to implement them.

Customary international law plays an important role in the present dispute, particularly in the cases against the nuclear weapon states not parties to the NPT. How much of nuclear non-proliferation law has become customary international law has been discussed elsewhere (see, for instance, here). Has Article VI, in particular, become binding on all states even beyond the NPT, as argued by the Marshall Islands? I am not persuaded by the applicant’s arguments. The fact that a treaty has been almost universally ratified is not, on its own, sufficient evidence of its customary status. To reach this conclusion, one has to look at the practice and opinio juris of the states not parties to the treaty: my feeling is that Israel, India, Pakistan and North Korea are going exactly in the opposite direction. Furthermore, even certain states parties (i.e., the five nuclear weapon states) have conducted themselves and expressed views that are difficult to reconcile with the alleged customary nature of Article VI. It is true that universality is not necessary for the formation of customary international law. However, it is not because there are a few states against in spite of a significant majority in favour that a custom corresponding to Article VI cannot be considered formed, but because the contrary practice and opinio come from those states that have nuclear weapons. To be clear, I am not referring to the doctrine of the persistent objector: I am not arguing that a custom in force is not applicable to certain states. My point is rather that a customary norm cannot sediment unless the practice and opinio juris of the specially interested states support this. The International Law Association’s 2000 Report on the formation of customary international law confirms that the extensive character of state practice is more a qualitative than a quantitative criterion: ‘if all major interests (“specially affected States”) are represented, it is not essential for a majority of States to have participated (still less a great majority, or all of them)’ (p. 26). Specially affected states are primarily those that had the opportunity to engage in the relevant practice. It is difficult to see, then, how Article VI can become customary international law without considering the practice and opinio juris of those states that possess nuclear weapons and to which the provision is primarily addressed. The fact that Article VI does not reflect customary international law is confirmed in the ICJ’s 1996 Advisory Opinion, where the Court states that the obligation ‘formally concerns the 182 States parties to the Treaty on the Non-Proliferation of Nuclear Weapons’.

It should be incidentally noted that, if Article VI is only a treaty obligation and not also a customary provision, it would be at best an obligation erga omnes partes, and not erga omnes as too hastily argued by the applicant. In other words, it is an obligation assumed towards the group of the states parties collectively considered, but not towards the international community as a whole.