June 26, 2025
The recent attack of Iran by Israel and the United States has once again raised important legal questions concerning the scope and possible evolution of the international law of self-defence.
Many commentators have immediately explained that this use of force is illegal, making in particular reference to Articles 2(4) and 51 of the UN Charter. The latter provision regulates “self-defence” as one of the three exceptions to the prohibition of the use of force under Article 2(4). In particular, it provides that there must be an “imminent” armed attack. It has been quite easily shown that, although probably illegal under the Treaty on the Non-Proliferation of Nuclear Weapons (which is a separate issue), it is very difficult to conclude that Iran’s nuclear activity constituted an “imminent” armed attack on Israel. For an exemplary explanation see Milanovic (2025):
“Even on very flexible understandings of imminence, it cannot be argued, on the evidence that is currently publicly available, that (1) Iran has decided to build a nuclear weapon, i.e. that its leadership intends to do so, and that (2) once the weapon is built, Iran intends to use it against Israel.”
In this brief post, I want to raise a few questions that follow on the premise that, under no possible interpretation, even a liberal one (in particular of the requirement of “imminence”), Article 51 of the UN Charter can be used to justify the Israeli/American use of force. These questions may be highly speculative and may/not be corroborated by the information publicly available/events in flux in current days. But, still, I believe, they are of great relevance to international lawyers and they should be dealt with … “imminently”! (To further strengthen the background to the questions, you can read the few, concise and to the point, pages written by Ronzitti almost 20 years ago.)
Questions:
- Premise 1: We are of course working on the premise that there is currently no war between Israel and Iran, i.e. that the issue is not a jus in bello one (see in this respect the speculation by Cohen and Shany (2025)). What we are confronted with therefore is a question pertaining jus in bellum.
- Premise 2: If it is accepted that Article 51 UN Charter is the positive (but not exclusive) expression of the “Inherent” right of self-defence that the Fathers inserted in the UN Charter, it is also accepted that this coexists with any entitlement to self-defence under customary law. (Additional premise: the sparse case-law of the ICJ does not really clarify this relationship.)
- What are the substantive law differences between the two, in particular with respect to the requirements that justify self-defence?
- What is the precise legal relationship between the treaty-law based entitlement and the customary-law based entitlement?
- Is it possible to have customary law going contra the Charter, for example sparing from the requirement of “imminence”? Or, indeed, corroborating an expansive concept of “imminence” (which may also inform the interpretation of Article 51 UN Charter, thus contributing to the alignment of these tow sources)?
- Perhaps worryingly for the strength of the prohibition of the use of force under Article 2(4) UN Charter, and pushing the balance to a point of political-legal equilibrium ante-UN Charter, are we assisting to an ever more significant divide in the opinion of States on the validity of pre-emptive action?
- Is there a new custom developing and permitting such pre-emptive use of force? (See in this respect the recent declarations of NATO Secretary-General Mark Rutte and declarations/omissions of key US allies.)
- If so, having a full spectrum of temporal/causal steps in pre-emptive action, can we already conceptualise what appears to be permitted/what not under this newly forming position? Is a threat enough? If so, how serious or credible should it be? What type of evidence does suffice, in particular with respect to nuclear weapons?
As I said, what I want to do with this skeletal post is simply to raise legal questions and provide a basic conceptual heuristic for further research. I don’t want to engage with the specific facts and/or their probative value. I don’t want to side with any party or provide any normative assessment on what is/not desirable. The sentiment motivating this blog post (like many others) is that we are indeed witnessing seismic changes which require us hard (perhaps new) thinking.
lucaslaws 