Would it be lawful in international law for a state to take military action to prevent another state from developing technology that can be employed to develop nuclear weapons?
International law recognizes no such right and any action by a State would be illegal. This is because international prohibits all use of force through Article 2(4). While, as discussed before, this does not include self-defence, which remains the legitimate right of all States, no such argument could be made in this scenario. The development of nuclear technology, even for military purposes, remains a legal right of States. The development of nuclear weapons is not an act of aggression, rather it is the sovereign prerogative of every state to develop and maintain armaments for defence purposes subject only to the legality of those weapons. Only a threat or actual use of force by a State would violate the line drawn by Article 2(4).
On a practical note, in order for such a rule to be created in international law that would permit the use of force under such circumstances, either an international agreement or a new custom would be required. The democratic character of international law means that if such a treaty were to be signed, it would only bind States that ratified it. As such only military action against these States would be justified. In order for a custom to develop in this regard, we would need consistent State Practice as well as Opinio Juris over a sustained period of time. Neither is likely to develop. The international community and the Security Council expressed their firm disapproval of any such doctrine or principle in the aftermath of Israel’s attack on the Orisak nuclear reactor in Iraq in 19841, through Security Council Resolution 487, which was passed unanimously and not only declared Israel’s actions illegal but also awarded compensation to Iraq.
It must also be pointed out that many States in the world possess nuclear weapons and the establishment of a principle that prevents the legitimate aspirations of other States in this regard would amount to an almost fatal blow to the concept of sovereign equality on which international order, law and comity have been so delicately poised for centuries now ever since the Treaty of Westphalia. Unless nuclear weapons in themselves are made illegal and equally unavailable to all countries, international law cannot be the foundation of any such permissive principle.
1 Operation Opera Orientalis