Explainer: Is Israel’s military action against Iran legal?

Inter­na­tion­al law dif­fers in nature from domes­tic law in many ways.

In Aus­tralia, domes­tic law con­sists of Acts of par­lia­ment and judg­ments in court cas­es which inter­pret and apply those Acts.

In con­trast, inter­na­tion­al law con­sists prin­ci­pal­ly of:

1. treaties which are con­tracts entered into by States and are legal­ly bind­ing only on the States which are par­ties to them, and
2. cus­tom­ary law, which are rules that have been inferred from the way States have act­ed in prac­tice and the opin­ions they have expressed about the legal effect of those prac­tices. Cus­tom­ary law rules can there­fore be hard to define, and they can change over time as the prac­tices of States change, and as their opin­ions about the legal­i­ty of those prac­tices change.

In inter­na­tion­al law there is noth­ing equiv­a­lent to an Act of par­lia­ment. The UN is not a par­lia­ment. It is a polit­i­cal forum that pass­es many res­o­lu­tions, the vast major­i­ty of which are not legal­ly bind­ing on mem­ber States. How­ev­er, the terms of those res­o­lu­tions can help to shape new rules of cus­tom­ary inter­na­tion­al law if they are gen­er­al­ly accept­ed by States with­out dis­sent.

The rules that apply to the resort to force by a State in self-defence against an exter­nal mil­i­tary threat were devel­oped in the nine­teenth cen­tu­ry, long before nuclear weapons were con­ceived let alone built. Under those rules, the exter­nal mil­i­tary threat has to be “immi­nent”. That is, the threat must be right on the point of devel­op­ing into an actu­al armed attack. Only then can the threat­ened State take mil­i­tary action to defend itself.

Applied strict­ly, this would mean that Israel could not take mil­i­tary action against Iran’s nuclear pro­gram until Iran actu­al­ly devel­ops a nuclear weapon and the means to deliv­er it. In the mean­time, Israel would sim­ply have to live with the threat of an Iran­ian regime that has open­ly and repeat­ed­ly com­mit­ted itself to Israel’s destruc­tion and has ille­gal­ly enriched ura­ni­um to lev­els of puri­ty that go far beyond what is need­ed for any peace­ful pur­pose.

No State would be pre­pared to live like that, under an ever-dark­en­ing shad­ow of anni­hi­la­tion. That is why there has been wide­spread accep­tance by most oth­er States, includ­ing Aus­tralia, of Israel’s strikes against Iran’s nuclear pro­gram. That accep­tance, rein­forced by the US’s own strikes against Iran’s nuclear facil­i­ties, con­sti­tutes new State prac­tice and legal opin­ion which is inform­ing the devel­op­ment of new rules of cus­tom­ary inter­na­tion­al law con­cern­ing a State’s right to resort to mil­i­tary force in self-defence against an exter­nal nuclear threat.

So the short answer to the ques­tion of whether Israel’s mil­i­tary action against Iran is legal is yes.