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Legality of the Threat or Use of Nuclear Weapons

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Overview of the case

By a letter dated 19 December 1994, filed in the Registry on 6 January 1995, the Secretary-General of the United Nations officially communicated to the Registry a decision taken by the General Assembly, by its resolution 49/75 K adopted on 15 December 1994, to submit to the Court, for advisory opinion, the following question : “Is the threat or use of nuclear weapons in any circumstance permitted under international law ?” The resolution asked the Court to render its advisory opinion “urgently”. Written statements were filed by 28 States, and subsequently written observations on those statements were presented by two States. In the course of the oral proceedings, which took place in October and November 1995, 22 States presented oral statements.

On 8 July 1996, the Court rendered its Advisory Opinion. Having concluded that it had jurisdiction to render an opinion on the question put to it and that there was no compelling reason to exercise its discretion not to render an opinion, the Court found that the most directly relevant applicable law was that relating to the use of force, as enshrined in the United Nations Charter, and the law applicable in armed conflict, together with any specific treaties on nuclear weapons that the Court might find relevant.

The Court then considered the question of the legality or illegality of the use of nuclear weapons in the light of the provisions of the Charter relating to the threat or use of force. It observed, inter alia, that those provisions applied to any use of force, regardless of the weapons employed. In addition it stated that the principle of proportionality might not in itself exclude the use of nuclear weapons in self-defence in all circumstances. However at the same time, a use of force that was proportionate under the law of self-defence had, in order to be lawful, to meet the requirements of the law applicable in armed conflict, including, in particular, the principles and rules of humanitarian law. It pointed out that the notions of a “threat” and “use” of force within the meaning of Article 2, paragraph 4, of the Charter stood together in the sense that if the use of force itself in a given case was illegal — for whatever reason — the threat to use such force would likewise be illegal.

The Court then turned to the law applicable in situations of armed conflict. From a consideration of customary and conventional law, it concluded that the use of nuclear weapons could not be seen as specifically prohibited on the basis of that law, nor did it find any specific prohibition of the use of nuclear weapons in the treaties that expressly prohibited the use of certain weapons of mass destruction. The Court then turned to an examination of customary international law to determine whether a prohibition of the threat or use of nuclear weapons as such flowed from that source of law. Noting that the members of the international community were profoundly divided on the matter of whether non-recourse to nuclear weapons over the past 50 years constituted the expression of an opinio juris, it did not consider itself able to find that there was such an opinio juris. The emergence, as lex lata, of a customary rule specifically prohibiting the use of nuclear weapons as such was hampered by the continuing tensions between the nascent opinio juris on the one hand, and the still strong adherence to the doctrine of deterrence on the other. The Court then dealt with the question whether recourse to nuclear weapons ought to be considered as illegal in the light of the principles and rules of international humanitarian law applicable in armed conflict and of the law of neutrality. It laid emphasis on two cardinal principles : (a) the first being aimed at the distinction between combatants and non-combatants ; States must never make civilians the object of attack and must consequently never use weapons that are incapable of distinguishing between civilian and military targets while (b) according to the second of those principles, unnecessary suffering should not be caused to combatants. It follows that States do not have unlimited freedom of choice in the weapons they use. The Court also referred to the Martens Clause, according to which civilians and combatants remained under the protection and authority of the principles of international law derived from established custom, the principles of humanity and the dictates of public conscience.

The Court indicated that, although the applicability to nuclear weapons of the principles and rules of humanitarian law and of the principle of neutrality was not disputed, the conclusions to be drawn from it were, on the other hand, controversial. It pointed out that, in view of the unique characteristics of nuclear weapons, the use of such weapons seemed scarcely reconcilable with respect for the requirements of the law applicable in armed conflict. The Court was led to observe that “in view of the current state of international law and of the elements of fact at its disposal, [it] cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake”. The Court added, lastly, that there was an obligation to pursue in good faith and to conclude negotiations leading to nuclear disarmament in all its aspects under strict and effective international control.

This overview is provided for information only and in no way involves the responsibility of the Court.