Few questions in contemporary international law have generated as much sustained controversy as the legality of anticipatory or pre-emptive self-defence. The debate, long simmering in academic writing, intensified dramatically after the attacks of 11 September 2001 and the subsequent articulation by the United States of a doctrine of pre-emptive action in its 2002 National Security Strategy. The idea traces back to the nineteenth‑century Caroline affair, where the United States argued that force may be used only when the necessity is “instant, overwhelming, leaving no choice of means, and no moment for deliberation.” This formulation appeared to impose a clear temporal limit for many decades: states could act only when an attack was truly imminent. Yet both the historical record and modern practice complicate that simplicity. Today, cyber capabilities, mobile missile units, proxy networks, and nuclear latency make the temporal markers once associated with “imminence” increasingly unstable.
These issues came sharply into focus on 28 February 2026, when the United States and Israel launched coordinated strikes across Iran against leadership targets, military infrastructure, missile sites, air defences, naval assets, and residual nuclear-related facilities. The operation was justified as necessary to neutralise an imminent threat and prevent Iran from obtaining a nuclear weapon. Iran responded with missiles and drones targeting US, Israeli and allied assets. In emergency sessions of the UN Security Council, the United States and Israel defended the strikes as lawful preemptive self-defence, while Iran, Russia, China, and several Arab states condemned them as violations of the Charter.
The central question is whether the operation was lawful under the jus ad bellum. What follows outlines the legal framework, applies it to the facts as publicly known, and then reflects on the broader implications for the future of the law.
I. The Legal Framework
The laws governing when the use of force is permitted in international relations are embodied in the Charter of the United Nations and in long-standing customary law. Article 2(4) of the UN Charter prohibits the threat or use of force against the territorial integrity or political independence of any state. There is no doubt that large-scale strikes on another state’s territory fall within this prohibition. The only potentially applicable exception is Article 51, which preserves the “inherent right” of self-defence if an armed attack occurs.
Much of the debate concerns the meaning of “armed attack,” the permissibility of acting before one occurs, and the conditions attached to any such anticipatory use of force. A narrow, Caroline-based form of anticipatory self-defence is often cited: necessity must be genuinely urgent, force must be strictly limited, and the threat must be clearly impending. Restrictionist readings argue that the Charter forecloses anticipatory action altogether. States such as the United States and Israel have taken a broader view, arguing that the reference to an “inherent right” preserves pre-existing custom and that strict textualism is ill-suited to modern threats. Whatever the position adopted, any self-defence claim is limited by necessity and proportionality, and these limits apply continuously as the operation unfolds.
Where non-state actors are involved, the threshold is particularly demanding. Support such as arming or financing a group may be an unlawful use of force, but it does not automatically constitute an armed attack. For that, the sponsoring state’s involvement must reach a level comparable to an attack by regular forces (as per the 1986 ICJ Nicaragua v. USA case). In addition, collective self-defence requires that the state supposedly being defended has itself been attacked or imminently threatened and has requested assistance. Article 51 also requires that measures taken in self-defence be reported to the Security Council immediately.
II. The Facts as Publicly Known
The strikes, described by the United States as “Epic Fury,” targeted leadership figures, missile production and launch sites, air defences, naval assets, and aspects of Iran’s nuclear-related infrastructure. US officials emphasised preventing nuclear armament and degrading missile capabilities; Israel described the operation as removing an existential danger.
These events occurred just after three rounds of US–Iran nuclear–related talks. Oman reported progress and suggested further technical discussions were expected at the IAEA within days. The UN Secretary‑General urged restraint and lamented that a diplomatic window had been “squandered.” At the Security Council, the United States and Israel maintained the operation was a necessary response to imminent threats; Iran denounced the strikes as unlawful aggression; Russia, China, and the Arab League warned of regional escalation and rejected any rationale involving regime change.
III. Applying the Law
A. Was there an armed attack by Iran?
On the public record, there is no evidence that Iran launched an armed attack on the United States or Israel immediately prior to the operation. Iran’s retaliatory strikes came after the operation began and cannot retrospectively justify them. If the United States relied on collective self-defence of Israel, it would need to demonstrate both that Israel had been attacked or faced an imminent attack and that Israel requested assistance. Whether either condition was satisfied remains unclear.
Iran’s past proxy activity does not automatically supply the missing element. Support for armed groups may be an unlawful use of force or intervention, but it constitutes an armed attack only when the supporting state’s involvement reaches a high threshold of scale and effects. Public statements by the United States and Israel focused not on attributing a specific armed attack to Iran on 28 February but on preventing future dangers. On that basis, the requirement of a prior or ongoing Iranian armed attack does not appear to be met.
B. Was an Iranian attack imminent?
US and Israeli officials asserted the existence of imminent threats tied to missile capabilities, naval forces, and nuclear ambitions. Yet active diplomacy in the days before the strikes complicates the claim that there was “no moment for deliberation.” Negotiations were underway, Omani mediation suggested progress, and technical discussions were reportedly imminent.
Those defending anticipatory force may argue that rapid‑activation systems—mobile launchers, cyber tools, decentralised proxy cells—leave defenders with little time to react and that traditional indicators of imminence no longer apply. On this account, stealth, speed, and deniability make it unreasonable to expect states to wait for clearer signs of an impending attack.
However, accepting this stance risks collapsing the distinction between anticipatory and preventive self-defence. Capacity, even destabilising capacity, is not the same as intention. Expanding “imminence” to include diffuse, long-term risks would transform Article 51 into a broadly permissive doctrine and diminish the protective force of Article 2(4). On the public record, the claim of imminence appears unsubstantiated and closer to preventive logic than to the narrow anticipatory model traditionally invoked.
C. Regime Change and Political Independence
A further difficulty lies in the transformative rhetoric surrounding the operation. Article 2(4) protects a state’s political independence. While self-defence may justify repelling an attack, it does not authorise the forcible reshaping of another state’s political order. When the stated objectives of a military campaign move from defending against a threat to encouraging or enabling internal political change, the defensive rationale becomes far less plausible. Past conflicts where such aims emerged—most famously Iraq in 2003—show the legal and political risks of allowing self-defence to bleed into regime‑change projects.
D. Necessity
Necessity asks whether force was the only reasonable means available to avert the threatened attack. This must be assessed in advance, based on what was reasonably known at the time. The existence of active negotiations and reported progress suggests that nonforcible alternatives remained available. That makes it difficult to argue that military action had become the only option.
The requirement to report self-defence measures to the Security Council also matters. How the United States and Israel described the threat sheds light on whether the operation was conceived as a limited defensive act or as part of a broader strategic enterprise. The timing and content of any Article 51 letters are therefore relevant to evaluating necessity and good faith.
E. Proportionality
Proportionality demands that the scale and effects of the defensive action correspond to the threat addressed. Even if an attack is imminent, the response must be confined to what is required to avert it. The breadth of Operation Epic Fury as a multi-theatre campaign targeting leadership, naval forces, missile production, and air defences, sits uneasily with this requirement. Such an expansive operation, with predictable region-wide escalation, exceeds what would ordinarily be expected if the aim were merely to forestall a specific, close-in strike. The gap between the asserted danger and the scope of the response makes it difficult to conclude that proportionality was met.
Taken together, the available evidence suggests that the operation does not meet the requirements of anticipatory self-defence. There was no clear prior armed attack; imminence is unproven; necessity is undermined by active diplomacy; proportionality is strained by the operation’s scale. Absent Security Council authorisation or Iranian consent, the strikes appear inconsistent with Article 2(4).
IV. Normative Drift
A final question is whether Epic Fury will reshape the law. When a powerful state asserts a broader right to strike first, the risk is that others will follow. Several states have adopted language in recent years that suggests more expansive defensive postures. Yet actual practice remains limited, inconsistent, and confined to a small group. Much of the international community continues to reject broad anticipatory doctrines.
International law evolves through state reactions. Endorsements, condemnations, or silence each contribute to shaping norms. If the response to Epic Fury is muted, the practice may begin to accumulate. If it is largely critical, the operation will likely be treated as another instance of preventive force operating outside the Charter without altering its structure.
V. Conclusion
The legality of the operation must be judged at the point of decision, not in hindsight. Strategic or political gains cannot retroactively legitimise a use of force that falls outside the Charter framework. Early signs of regional spill-over and diplomatic rupture only emphasise the stakes. The challenge is not only to evaluate whether this operation was lawful, but also to recognise how episodes like this influence the future evolution or erosion of the laws governing the international use of force.
Noga Glucksam teaches on MA International Relations.
