Julian Ku is professor of constitutional law at Hofstra University.
When Yale law professor Oona Hathaway calls U.S. strikes on Iran “blatantly illegal,” she speaks for a large segment of the international legal academy. For many scholars, the analysis is straightforward: The U.N. Charter prohibits the use of force except in self-defense against an armed attack or with Security Council authorization. Neither condition, they argue, is satisfied. Case closed.
There are plausible counterarguments. The U.S. government has long maintained that sustained attacks by Iranian-backed militias can trigger the “inherent right of individual or collective self-defense.” Some contend that where a state directs, supports or is “unwilling or unable” to halt proxy attacks, use of force in its territory may be justified. Others point to evolving state practice that has stretched the traditional understanding of imminence and attribution.
But the more natural reading of the Charter is a narrow one. Article 2(4) bars the use of force against another state’s territorial integrity or political independence. Article 51 preserves self-defense “if an armed attack occurs.” The text’s plain meaning is restrictive. On that reading, cross-border strikes on Iran absent clear attribution of an armed attack to the Iranian state are difficult to reconcile with the Charter’s design.
If that is right, however, the more important story is not American lawbreaking. It is the intellectual complacency of the legal framework itself — and of the lawyers who defend it.
International law governing the use of force has ossified into a formal binary. A strike is either lawful or unlawful. There is little space in the doctrine to distinguish among profoundly different uses of force. Under a strict reading, Russia’s full-scale invasion of Ukraine and a limited U.S. strike aimed at deterring Syria’s use of chemical weapons are both illegal. NATO’s intervention in Kosovo — undertaken to halt ethnic cleansing — is likewise condemned as a Charter violation. Meanwhile, the Charter has strikingly little to say about catastrophic internal wars in Sudan or Myanmar. And its application to a potential Chinese invasion of Taiwan would turn on technical questions of recognition and statehood that might even favor China’s aggression.
This flattening effect is not a minor doctrinal quirk. It is a credibility problem.
The problem is not that governments ignore international law. It is that international lawyers have too often retreated into a rigid formalism that refuses to grapple with moral and strategic differences everyone else can see.
There are good reasons to defend a bright-line prohibition on force. The Charter’s narrow structure was designed to reduce opportunistic claims of self-defense and to cabin unilateral war-making. But the choice is not between bright lines and moral chaos. It is between a legal discourse that candidly engages with normative distinctions and one that hides behind textual minimalism while reality moves on.
Over the past two decades, many scholars have tried to preserve the Charter’s architecture by quietly stretching its exceptions — loosening standards of imminence for threats, normalizing “unable or unwilling,” or lowering thresholds for attribution. That strategy is unsustainable. It allows powerful states to reshape doctrine through practice while academics insist that nothing fundamental has changed. It is doctrinal drift masquerading as fidelity.
A more honest approach would acknowledge that the jus ad bellum — conditions under which states may resort to war — already rests on moral judgments. We distinguish instinctively between Russia’s attempt to erase Ukrainian sovereignty and other, more limited uses of force such as last summer’s U.S. attack on Iran’s nuclear facilities. We distinguish between humanitarian interventions and wars of conquest, between defensive necessity and strategic opportunism. The law should be capable of articulating those differences rather than pretending they do not matter.
That requires international lawyers to move beyond a mechanical lawful-unlawful calculus and to develop a more openly normative framework — one that assesses the gravity (and not just the imminence) of the threat, the necessity and proportionality of the response in light of the speed and complexity of modern warfare, the risks to civilians, and the systemic consequences for international order.
The U.S.-Israeli strike on Iran arguably falls on the wrong side of the Charter’s traditional interpretation. But if that conclusion leaves the law unable to differentiate meaningfully between the Ukraine and Iran conflicts, the problem runs deeper than any single episode.
International law’s authority ultimately depends on its ability to align legal judgment with widely shared moral intuitions about war and peace. If it cannot do that — if it insists on treating profoundly different conflicts as doctrinally interchangeable — it will not meaningfully constrain powerful states. Nor will it command the moral clarity needed to condemn genuine aggression when it occurs.
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