On February 28, the world woke to the news that the United States and Israel had executed a coordinated attack on Iran, targeting important military and nuclear sites and killing several senior military and government members including the nation’s supreme leader Ayatollah Ali Khamenei.

Dubbed “Operation Epic Fury,” the attack was carried out without prior authorization by the U.S. Congress. It has resulted in a strong response by Iran, with missile and air strikes across the region, including in Israel, Bahrain, Saudi Arabia, Qatar, the United Arab Emirates, and Iraq—with casualties including American.

Here, Stanford Law’s Allen Weiner, an expert in international law, discusses the legality of the attack and what might happen next.

What justification did President Trump offer for the coordinated attack on Iran by the U.S. and Israel?

President Trump, in his February 24 State of the Union address and his February 28 video comments announcing the attacks against Iran, identified a number of purported justifications for attacking Iran.  There is a strong moral valence to the President’s remarks; he referred to the Iranian regime as a “vicious group of very hard, terrible people.”  The President also cited a number of historical grievances against Iran, going back to the 1979 Tehran Embassy hostage-taking and Iran’s support for anti-American militias during the post-2003 American occupation of and subsequent military presence in Iraq.  President Trump also highlighted Iran’s longstanding support for terrorist groups and its repression of its own population.

In terms of key security threats that President Trump said Iran poses to the United States and its allies, he asserted in his February 28 remarks that U.S. military actions were aimed at “eliminating imminent threats from the Iranian regime.”  In that regard, President Trump emphasized Iran’s nuclear program, which he said involves the “pursuit of nuclear weapons.” The President also pointed to Iran’s significant missile program, including the development of long-range missiles which he asserted “can now threaten our very good friends and allies in Europe, our troops stationed overseas, and could soon reach the American homeland.”  (Contrary to President Trump’s statement, a 2025 assessment by the Defense Intelligence Agency assessment indicated that Iran does not currently possess ballistic missiles capable of hitting the United States; the agency estimated that it might be able to create an arsenal of up to 60 intercontinental ballistic missiles by 2035 “should Tehran decide to pursue the capability.”)

Does that justification meet legal standards? Was the attack “legal”—in the U.S. and international frameworks?

From an international law perspective, my judgment is that the attack was quite clearly illegal.  Under the United Nations Charter, states are prohibited from using force in international relations except in one of two circumstances: (1) where the state acts in self-defense if it has sustained an “armed attack” by its adversary; or (2) where the U.N. Security Council has authorized the use of force.  The Security Council has not, of course, authorized the use of force against Iran.  In terms of self-defense, Iran did not carry out an armed attack against the United States.

With regard to the right of self-defense, there are international legal scholars—and I count myself as a member of this camp—who believe that states can exercise the right of self-defense not only after they have sustained an armed attack, but where they face an imminent threat of attack.  This is referred to by international lawyers as “anticipatory self-defense,” and President Trump gestured to this concept by stating that the U.S. attacks against Iran were aimed at “eliminating imminent threats from the Iranian regime.”  The problem with this position is that even if there is a right of anticipatory self-defense, the predicate condition is strict; it requires an imminent threat of an armed attack by the adversary.  The notion that Iran presents a general security threat to U.S. interests does not constitute a threat of imminent attack.  Nor does the possibility that Iran might at some point in the future acquire either nuclear weapons or intercontinental missiles capable of reaching the U.S. homeland amount to a threat of an imminent attack.

There are also issues about whether the U.S. attack against Iran is consistent with domestic law regarding the allocation of powers between the President and the Congress regarding decisions to use force.  Article I, Section 8, Clause 11 of the Constitution confers the power to “declare War” on the Congress, but the President is the Commander-in-Chief and U.S. Presidents have, over the centuries, exercised the use of force abroad more than 100 times without congressional authorization.

What is the administration’s position regarding the President‘s authority to launch the attack without congressional approval?

The Justice Department’s Office of the Legal Counsel has taken the position that an armed conflict amounts to “war in the constitutional sense,” i.e., in the sense of requiring congressional authorization, only if the conflict involves “prolonged and substantial military engagements, typically involving exposure of U.S. military personnel to significant risk over a substantial period.”  Given the historical record of the exercise of force based solely on presidential action, it would be difficult to argue that the attacks against Iran so far meet the standard of what would require congressional authorization.  President Trump has indicated, however, that the military campaign is expected to last “four to five weeks,” but “possibly far longer than that.”  He has also indicated that he has not ruled out the deployment of U.S. ground troops in Iran.  The longer and more intense the military campaign becomes, the stronger the argument that the use of force requires congressional approval becomes.

Can you talk about the war powers? It has been reported that Democrats are pushing to consider war powers resolutions—but the likelihood of anything passing right now seems low.

My answer to the previous question focused on the constitutional allocation of war powers between the Congress and the President.  But your question also raises questions about the War Powers Resolution, a statute the Congress adopted in 1973, at the end of the Vietnam War, in an effort to ensure that Presidents did not commit the United States to war without congressional authorization.  The War Powers Resolution requires the President to notify the Congress whenever U.S. troops are “involved in an attack or hostilities.”  The law provides that if Congress does not, within sixty days after receiving such a notification (or ninety days if the President avails himself of procedures providing for an extension of that deadline), declare war or otherwise authorize the use of force, the President is legally obligated to “terminate” that use of force.  Although the Executive Branch has consistently since 1973 asserted that the War Powers Resolution constitutes an unconstitutional infringement on the President’s Commander-in-Chief powers, most presidents have at least submitted the reports required by the law when U.S. forces are introduced into hostilities.

Whatever the constitutional status of the War Powers Resolution may be, if Congress opposes the military campaign against Iran, it certainly could enact legislation that would prevent the President from continuing that military campaign.  Although there are divergent views about the allocation of war powers between the Congress and the President, there is little doubt that the Congress could enact a law prohibiting the expenditure of any funds related to military operations against Iran.  Congress has enacted such laws on a number of occasions in the past.  But the Congress has historically been very reluctant to exercise its powers to prohibit the President from waging war, and the prospects that it will do so at a time when the Republican party holds a majority in both houses of Congress seem quite unlikely to me.

Can you talk about the potential dangers, to the U.S. and its allies, if the legal guardrails we have in place regarding the use of force are breaking down?

The attitude of the current administration towards international law and its actions pose a dangerous threat, in my mind, to the legal regime adopted in the U.N. Charter in 1945 to restrict the use of force in international relations.  Prior to the 20th century, there were very few substantive restrictions on the right of states to use force.  States in essence had the right to use force to address violations of their rights, or perceived wrongs.  There were procedural prerequisites for going to war—mainly, that states had to articulate their demands and seek redress through diplomatic means—but the right to go to war was a sovereign right, unrestricted by any treaty or customary international law rules.  Under this regime, during the 18th, 19th, and 20th centuries, war was a regular part of international relations.  In other words, the law tracked the maxim of the Prussian theorist of war Carl von Clausewitz that “war is the continuation of politics by others means.”  The result of that legal regime, as we know, was the frequent waging of war among states in the international system which, given changing technologies, by the 20th century produced wars that resulted in extreme levels of destruction and suffering.

Since the adoption of the U.N. Charter and its prohibition on the use of force in international relations, the level of interstate wars in the international system has declined.

President Trump appears not to care very much about the international legal regime governing the use of force.  In a January 2025 interview with the New York Times, he stated, when asked about what limits he recognized on the assertion of power by the United States, he answered: “My own morality. My own mind. It’s the only thing that can stop me.”  And, he added, “I don’t need international law.”

This strikes me as an alarming reversion to the Clausewitzian vision of the international use of force as “the continuation of politics by other means.”

One can expect that if the United States, which was perhaps the leading architect of the U.N. Charter’s regime on the use of force, decides that states can go to war whenever they perceive it to be in their interest, other states will do so, as well.  Russia, of course, already demonstrated its disregard for the prohibition on the use of force through its 2014 invasion of Crimea and later its 2022 full-scale invasion of Ukraine.  If the world’s most powerful countries conclude, in effect, that they can engage in the international use of force whenever they believe it to be in their interests to do so, the result will be the demise of the legal regime that has for 80 years been quite effective in reducing the level of interstate violence in the international system.  A return to the legal regime that led to the pervasive use of force in international relations and the devastating wars of the 20th century would not be in the long-term interests of the United States – or other states in the international system.

You’ve written about the interplay of international and national interests—and the tradeoffs countries make to maintain peace and all the benefits that peace brings. Can you talk about that?

President Trump’s professed lack of interest in international law seems grounded in the notion that international law is somehow incompatible with the pursuit of U.S. national interests.  As a reflection of that assumption, shortly after assuming office in 2025, he issued an Executive Order that, among other things, required to Secretary of State to conduct a review of “all conventions and treaties to which the United States is a party, to determine which … are contrary to the interests of the United States.”  A belief that international law is somehow at odds with U.S. national interests was also reflected in recent remarks by the United States Trade Representative, Jamieson Greer.  He said that the United States’ adherence to international law—in his remarks, he referred to the so-called “rules-based order”—“may lead to negative outcomes.  If we are overly rigid, we can end up tying our hands behind our back when we need to act in the national interest.”

I have a different view of the relationship between international law and the national interest.  As I suggested in an OpEd published in The Hill in April 2025, it is important to recall that international law is a consent-based regime, which means that states for the most part are bound only by those restrictions they freely accept.  States accept restrictions on their freedom of action because they believe the benefits of reciprocal limits on the freedom of states to act (such as forgoing the freedom to arrest foreign diplomats, or to expropriate foreign-owned property without just compensation, or to intentionally target civilians or mistreat prisoners of war during wartime) will produce benefits for themselves and for the global order.  With respect to the use of force, states in 1945 accepted limits on the pre-Charter right to use force in their international relations because they sensibly concluded that a world in which states would be barred from freely using force against one another would be one that advanced their long-term, systemic interest in a stable international order.  As I suggested in my OpEd in The Hill:

[G]iven the consent-based nature of international law, a country’s decision to become party to a treaty, even one that imposes some limitations on its freedom of action, is not a restriction on sovereignty. Instead, it is an exercise of its sovereignty, one that allows a country to gain the benefits of international cooperation, including greater security and prosperity. Rather than infringing America’s national interest, international law is a tool to advance it.

President Trump, in his January 2026 interview with the New York Times, said that he doesn’t need international law.  That, in my view, is a very short-sighted perspective.  If we want to secure the benefits of a world in which states do not use force against one another whenever they believe doing so would be in their interests – if we want to avoid the “scourge of war” that has “brought untold sorrow to mankind,” which the U.N. Charter’s legal regime on the use of force was meant to prevent—then the United States needs international law very much indeed.

Allen S. Weiner JD ’89, is an international legal scholar whose research and teaching focus primarily on the fields of international security and international conflict resolution. He also studies the challenges of online misinformation and disinformation. In the international security realm, his work spans such issues as international law and the response to contemporary security threats; the relationship between international and domestic law in the context of armed conflict; the law of war (international humanitarian law); just war theory, and international criminal law (including transitional justice). He is the director of the Stanford Program in International and Comparative Law; director of the Stanford Humanitarian Program; and director of the Stanford Center on International Conflict and Negotiation.