35 Fall 2026 y remarks are dedicated to the jus ad bellum dimensions of Israel’s war with Iran — that is, the legality of the resort to force itself. My focus is primarily on the initial decision by Israel and the United States to use force on February 28, 2026. This focus should not be misunderstood: it does not mean that I regard Iran’s response to the force used against it as legal. On the contrary, there is broad consensus among international lawyers that the Iranian response violated jus ad bellum, and Security Council Resolution 2817 already confirms that. I want to touch on two dimensions. First, what are the possible legal justifications for the use of force by Israel and the United States? Second, I want to examine the very significant gap between the emerging consensus in the international law academic community — which has been decidedly negative about the legality of the war — and the mild reaction of states to the same events. Possible Justifications for the Use of Force I begin with the question of justification. The vast majority of international law scholars have taken the position that the attack by Israel and the United States on February 28, 2026 violated the prohibition against the use of force. The reasoning in support of this conclusion is straightforward: there was no Security Council authorization for the U.S.-Israel operation, and as for self-defense, no Iranian armed attack was taking place at the time of the strike. Even under the doctrine of anticipatory self-defense, one must demonstrate the imminence of an attack — and here the claim is that there was no indication whatsoever that an Iranian attack on another country was imminent. Against this consensus, two arguments have been advanced, and I consider each in turn. The first argument invokes the concept of preventive self-defense — the idea of confronting threats before they become imminent. Although most international lawyers, if not almost all of them, reject the use of force in anticipation of long-term threat, one narrow exception is sometimes alleged: Between imminence and pure prevention lies a middle category involving a “last window of opportunity.” This happens when a state faces a long-term threat, and the moment to act against it is closing. Such a scenario is effectively what Israel argued in 1981 regarding its operation against the Osirak reactor in Iraq. But we should recall that at that time, the Security Council did not accept the argument. And on the facts of the present case, even this argument is difficult to sustain. It is hard to accept that in June 2025 the two leaders, Donald Trump and Benjamin Netanyahu, proclaimed that the Iranian nuclear program had been obliterated — and then, only eight months later, they return to tell us that an Iranian attack is imminent, or that we face a last window of opportunity to destroy (again) the Iranian nuclear program. The 2025 and 2026 positions do not sit comfortably together. The second approach, which I consider somewhat stronger legally, revolves around the argument that Israel and Iran were already involved before February 28, 2026, in ongoing hostilities. One can argue that from October 7, 2023 onwards — when the Iranian proxies started a war, which Iran itself joined directly on two occasions (April 13, 2024 and Oct. 1, 2024) — Israel was in a state of armed hostilities with Iran. If that is the case, then one could argue that following the June 2025 “twelve day war,” the conflict, or armed attack, had not really ended. A war is often comprised of a series of military operations, and once you are in a state of war, you do not need to justify each individual strike against your adversary anew. The challenge for this argument is the ceasefire agreed upon between Israel and Iran on June 23, 2025. What are we to make of it? Perhaps relevant is the fact that this ceasefire was composed of a single tweet by Donald Trump on Truth Social — an extremely thin basis on which to rest the claim that hostilities were terminated, notwithstanding the continuation of hostile threats by Iran against Israel. It is noteworthy that the Americans, for their part, have The Jus ad Bellum Dimensions of the War with Iran Yuval Shany M
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