On February 28, the United States Armed Forces launched Operation Epic Fury with a set of clear objectives: to “[d]estroy Iranian offensive missiles, destroy Iranian missile production, destroy [Iran’s] navy and other security infrastructure,” and, finally, ensure that Iran “will never have nuclear weapons.”
Epic Fury is only the latest round of an ongoing international armed conflict with Iran. As the United States has explained in multiple letters to the U.N. Security Council, including most recently on March 10, the United States is engaged in this conflict at the request of and in the collective self-defense of its Israeli ally, as well as in the exercise of the United States’ own inherent right of self-defense.
Critics have argued that the United States’s combat operations are inconsistent with the UN Charter. In truth, the United States is acting well within the recognized contours of international law relating to the use of force and self-defense. This legal assessment is grounded in facts demonstrating Iran’s malign aggression over decades, particularly in Iran’s escalatory attacks against the United States, Israel, and others in the region for years, which precipitated an international armed conflict that predated U.S. combat operations on February 28 and that continues to this day.
I. Iran’s Attacks on the United States, Israel, and Others
Any serious legal assessment of U.S. combat activities must be anchored in the relevant material facts. Beginning with its founding in 1979, the Islamic Republic of Iran has regularly attacked the United States, its interests, and its allies, including but not limited to Israel, directly and through proxies. The regime’s “revolutionary” Islamic ideology has been the justification for its decades-long pattern and practice of international terrorism and military adventurism, as well as its multibillion-dollar investments in developing the “Axis of Resistance” and ballistic missile, drone, and nuclear capabilities.
First, Iran is responsible for countless armed attacks against the United States, both through its own military and through its partners and proxies. As context, Iran’s hostility toward the United States began with the 1979 Revolution, subsequent sacking of the U.S. Embassy in Tehran, and the abuse and torture of American hostages for 444 days. It continued throughout the years that followed—from the bombing of the U.S. Marines in Lebanon in 1983, which killed 241 U.S. service members; to the Khobar Towers assault in 1996, in which 19 U.S. service members were killed and 500 other individuals were wounded; to the direction of IED attacks against U.S. soldiers in Iraq, which killed at least 600 Americans over a period of eight years.
Iranian-sponsored attacks against the United States intensified in 2019. Kata’ib Hezbollah (KH) and other Iran-aligned militias receiving support from and sometimes acting under the direction of the Iranian Revolutionary Guard Corps (IRGC) fired rockets at bases in Iraq where U.S. personnel were located, including in an attack that killed a U.S. contractor and injured Iraqi military officers in December 2019. KH also organized a 2019 attack, approved by the IRGC, against the U.S. Embassy in Baghdad that inflicted significant damage, and senior U.S. government officials concluded at that time that the IRGC was actively developing plans for further attacks against U.S. military personnel and diplomats in Iraq and throughout the region. The United States responded in self-defense with a targeted strike that killed IRGC Commander Qasem Soleimani, but Iranian armed attacks continued. Between 2021 and 2024, there were well over 100 attacks against U.S. personnel and facilities in Iraq and Syria by the IRGC and its partners and proxies. All the while, Iran continued to publicly reiterate and privately pursue its lethal plotting operations against both U.S. officials and private citizens.
Second, the regime has for decades maintained a clear and public position that Israel must be annihilated.[1] To that end, the Islamic Republic has devoted massive human and financial resources in pursuit of this goal. The regime has organized, funded, and supported terrorist attacks against Jews, Israel, and Israeli interests worldwide. Following October 7th attacks against Israel by the Islamic Republic-funded, trained, armed, and supported terrorist organization Hamas,[2] Iran attacked Israel directly, launching historically massive direct and indiscriminate ballistic missile strikes and drone swarms in April and October 2024.
The armed conflict between Israel and Iran has been ongoing since at least that point, and likely years earlier, as Israel underscored in its March 10, 2026, letter to the Security Council. Adding to the threat posed by these direct assaults on Israel, Iran has developed an illicit nuclear program that, if it led to the production of a nuclear weapon, would pose an immediate and present danger to the very existence of the State of Israel when coupled with Iran’s massive and expanding ballistic missile delivery capabilities.[3]
Third, Iran’s extensive, long-term support of Hizballah, Hamas, the Houthis, and various Iran‑aligned militia groups in Iraq and Syria has enabled those terrorist organizations to carry out destabilizing attacks against Israel, the United States, Argentina, and others, including countries seeking to freely exercise transit rights through the Strait of Hormuz. While the regime has, at times, concealed its role in certain attacks of this nature, the United States has established Iranian direction, control, and even active participation as a co-belligerent in some of the operations of those groups, as the United States explained in a February 5, 2024 letter to the Security Council. Furthermore, the Islamic Republic’s financial, equipment, training, and operational support for these terrorist organizations has intentionally empowered these groups to sow chaos in the region.
In late 2024, President Trump was again elected. During the early months of the second Trump Administration, the United States initiated negotiations in an intensive effort to resolve the underlying root causes of the ongoing conflict: the longstanding threat posed by Iran to U.S. interests in the region, including its continued proxy attacks on U.S. personnel and facilities and its illicit nuclear and ballistic missile programs. By June of 2025, however, it was clear that these efforts were fruitless.
II. An Analysis of the U.S. Response
Over many years, the Iranian regime engaged in a clear pattern of unprovoked aggression and direct and proxy attacks against Israel and the United States, while concurrently spending billions of dollars to operationalize its promise to destroy the former and continuously calling for “death” to the latter. That conduct established the factual basis and operative context for Operation Midnight Hammer, the U.S. military action that supported Israel in efforts to obliterate Iran’s nuclear program in June 2025. As indicated in its June 27 letter to the Security Council, the United States decided to act against the regime in collective self-defense of Israel, which, as described above, was undeniably already exercising its right of self-defense in response to an ongoing international armed conflict with the Islamic Republic. The June 27 letter built upon nine previous letters transmitted by the United States to the Security Council since 2021, including on February 27, 2021; June 29, 2021; August 26, 2022; March 27, 2023; October 30, 2023; November 14, 2023; November 28, 2023; December 29, 2023; January 26, 2024; and February 5, 2024.
Accordingly, the United States had an independent legal justification as a matter of jus ad bellum principles to enter into the conflict. But, as noted above, defensive U.S. actions could equally have been considered part of an ongoing international armed conflict between Iran and the United States itself, in which the United States was exercising its own, individual right of self-defense.
Some have argued that whatever the nature of the conflict with Iran that existed in June 2025, that conflict ended following the close of Operation Midnight Hammer, and that any further use of force must be considered a “fresh” use of force and justified anew under the jus ad bellum principles. But those critics have largely failed to acknowledge the facts—the clear pattern of ongoing Iranian attacks against the United States, Israel, and others in the region described above; the massive expansion of the regime’s offensive drone and ballistic missile capabilities; and its accelerated nuclear development—or to squarely address the legal question concerning when a conflict, once commenced, ceases.
According to the Department of War’s Law of War Manual, hostilities end when “opposing parties decide to end hostilities and actually do so, i.e., when neither the intent-based nor act-based tests for when hostilities exist are met.”[4] Similarly, according to the International Committee of the Red Cross, the legal test for whether an international armed conflict has ended is whether, based on an assessment of the facts on the ground, there has been a “general close of military operations” that has ended military movements of a bellicose nature “so that the likelihood of the resumption of hostilities can reasonably be discarded.”[5] Any assessment of whether an armed conflict has ended must be fact-based, taking into account both the intentions and the actions of the parties to the conflict.
Under either articulation of the customary international law standard for determining when an armed conflict has ended, the facts clearly support the proposition that the international armed conflict involving Iran, Israel, and the United States that was the subject of the June 27 Article 51 letter is ongoing.
As a threshold matter, the intense but ultimately fruitless attempts at negotiations by the United States in the first few months of the Trump administration, and again in late 2025 and early 2026, did not bring about an end to the conflict brought about by Iran’s continuing pattern of attacks between at least 2019 and 2024. States that attempt in good faith to resolve their disputes by peaceful means do not have their legitimate right of self-defense against an adversary extinguished by genuine but unsuccessful attempts to end a conflict. It was only after multiple attempts at negotiation failed that the United States resumed operations in this conflict.
Further, there is no evidence that any of the parties—Iran, Israel, or the United States—intended or decided to end either of the armed conflicts described above after the June 2025 operations. The parties did not make unilateral declarations concerning an end to hostilities, nor did they conclude any agreement related to the end of hostilities. After the June 2025 strikes, the parties observed a ceasefire to allow diplomatic negotiations to address the Islamic Republic’s continuing threat to the United States, Israel, and the region, but those negotiations failed. As was widely reported in the media, all parties—including Iran—continued to actively plan for further military engagements if diplomacy failed. The pause in hostilities during this period thus lacked the “stability” and “permanence” that must, as a matter of international law, be present to indicate an end to hostilities.
This legal approach is not, as some may argue, a conflation of the jus ad bellum and the jus in bello. For one, for purposes of a jus ad bellum analysis, there is no legal significance to the fact that the United States sent both a new notification to Congress under the War Powers Resolution and an Article 51 letter to the UN Security Council after operations resumed on February 28. Indeed, it is longstanding U.S. practice to submit such communications to both Congress and to the Security Council in situations where it is taking actions within the context of an ongoing armed conflict, and there are many such examples of it doing so.
But more fundamentally, if a conflict has not ended, then it must be ongoing. As a matter of international law, there is no requirement to continually reassess the jus ad bellum principles of necessity and proportionality in the context of an ongoing armed conflict. As former State Department Legal Adviser Brian Egan stated, “once a State has lawfully resorted to force in self-defense against a particular armed group following an actual or imminent armed attack by that group, it is not necessary as a matter of international law to reassess whether an armed attack is imminent prior to every subsequent action taken against that group, provided that hostilities have not ended.”[6] That principle applies equally once the United States has acted in self-defense against another State.
Even assuming arguendo that there was a jus ad bellum requirement to continually assess necessity and proportionality, those customary international law principles are satisfied here because of the scale and continued nature of the threat posed to the security of the United States and Israel. As the United States has previously explained: “A proper assessment of the proportionality of defensive use of force would require looking not only at the immediately preceding armed attack, but also at whether it was part of an ongoing series of attacks, what steps were already taken to deter future attacks, and what force could reasonably be judged as needed to successfully deter future attacks.”[7] Proportionality does not require that a State exercising its right of self-defense must use the same degree or type of force used by the attacking State in its most recent attack. Indeed, even if initial attacks are limited in scope but the attacking State continues to present a significant threat or to perpetrate further attacks specifically calibrated to avoid a larger response, the defending State may be justified in responding through an operation sufficient to decisively end the conflict.
Consistent with that understanding, the United States also noted in its communication to the Security Council that any assessment of the imminence, gravity, and scope of the threat posed by the Iranian regime would need to account for the decades of consistently malign foreign and domestic conduct and the dangerous and destabilizing risks of nuclear weapons and ballistic missiles in Iran’s hands. While the United States does not rely on a theory of imminence to justify its actions in this case—as described above, the United States believes that it and Israel were already engaged in an ongoing armed conflict with Iran as a result of the latter’s attacks—these factors are critically important in providing context for ongoing military operations.
Indeed, any legal analysis or process for determining the imminence of an attack and the proportionality of a potential response should account for the immense destructive power of nuclear weapons, the danger posed by ballistic delivery systems, the conduct of the relevant State actor, and the likelihood of other opportunities to mitigate the threat in the future.[8] The fact that these weapons are often developed in secret magnifies the potential danger to other States, which may not have the relevant intelligence reporting or opportunity to take measures to protect themselves against the potential use of such weapons before they are deployed. In considering the “imminence” of a nuclear attack, policy makers may also weigh the duration and gravity of repeated, public threats to eradicate other States and associated conduct, as well as defiance of international safeguards and attempts to develop capabilities to deliver a nuclear device. These statements and actions repeated over decades are often assertions of foreign policy objectives, not mere political slogans.
III. Conclusion
The operations recommenced in late February were part of an armed conflict with Iran that has been ongoing for years and, at the very least, since June 2025. Under well-established rules of international law, it is reasonable to conclude that this conflict did not end in the interim. And in an ongoing conflict, it is not necessary as a matter of international law to reassess whether an armed attack is imminent prior to every subsequent action taken against an adversary. Nor it is necessary to re-apply jus ad bellum standards of necessity and proportionality, although the actions taken by the United States would satisfy those principles if reapplied.
The United States has acted well within its international law obligations with respect to its use of force since operations began in late February. Iran, by contrast, has acted as any reasonable observer would have expected—lashing out against its neighbors, targeting Israeli civilians, murdering its own people, unlawfully closing the Strait of Hormuz, and wreaking havoc throughout the region. The regime’s outrageous, albeit predictable behavior only further underscores the fundamental necessity, utility, reasonableness, and lawfulness of Operation Epic Fury’s mission and goals.
[1] Prior to 1979, Iran and Israel maintained amicable relations. However, the Islamic revolution completely reversed this relationship. Ayatollah Ruhollah Khomeini, the founder of the Islamic Republic, denounced Israel as an illegitimate “Zionist regime” and severed all diplomatic relations. He wrote: “If the rulers of the Muslim countries truly represented the believers and enacted God’s ordinances, they would set aside their petty differences, abandon their subversive and divisive activities, and join together like the fingers of one hand. Then a handful of wretched Jews (the agents of America, Britain, and other foreign powers) would never have been able to accomplish what they have, no matter how much support they enjoyed from America and Britain.” Since then, calls for Israel’s total destruction have been deeply embedded in official rhetoric, military programs, state-sponsored education, and symbolic events such as Quds Day.
[2] According to a West Point Center for the Study of Terrorism monograph, “there is little doubt that Iran’s financial aid, structuring of its proxies into more cohesive armed factions and then into umbrella organizations, and assistance through the supply of weapons increased the deadliness and extremism of its Palestinian proxies.” Without Iranian assistance and nurturing, these groups would not have been able to strike Israel as they did—armed capabilities supplied by Iran, such as a variety of UAV designs, rockets, demolition charges, and other munitions, were smuggled into Gaza and used to deadly effect. In summary, “Iranian assistance allowed its Palestinian proxies to amass the firepower, messaging know-how, and much of the hi-tech equipment necessary to carry out and propagandize the attack. Financial aid provided by Iran did more than keep Hamas operating as a governing body in Gaza; it was also directly piped into Hamas’ terror and military apparatus.”
[3] International law must acknowledge the uniquely destructive power of ballistic missiles with nuclear weapons. The inherent right to self-defense cannot rationally be construed to require a State to wait until a self-avowedly hostile actor has a nuclear warhead-tipped missile ready to launch before lawfully taking a disabling strike. Indeed, hesitation under these circumstances would render self-defense futile—practically speaking, the last effective opportunity to defend a civilian population from a nuclear attack by the Islamic Republic or other rogue regime would be before it obtains a nuclear weapon and the ability to attack with it. Any contrary rule would undermine deterrence and reward aggression.
[4] As further explained in the Law of War Manual, the usual indicators for a determination of termination include an agreement to end hostilities, usually in the form of a peace treaty; a unilateral declaration of one of the parties to end the war, provided the other party does not continue hostilities; the complete subjugation of an enemy State and its allies; or a simple cessation of hostilities. Law of War Manual, Sec. 3.8.1.
[5] See “Frequently Asked Questions: International Armed Conflict,” at https://www.icrc.org/en/article/faq-international-armed-conflict: “The declassification of conflicts must be based on the facts on the ground analyzed in light of the applicable IHL legal criterion. For the ICRC, this criterion is the general close of military operations. Hostilities must end with a degree of stability and permanence for the IAC to be considered terminated. A general close of military operations means not only the end of active hostilities, but also the end of military movements of a bellicose nature, including those that reform, reorganize or reconstitute, so that the likelihood of the resumption of hostilities can reasonably be discarded.”
[6] Brian Egan, International Law, Legal Diplomacy, and the Counter-ISIL Campaign, Speech at the American Society of International Law (April 1, 2016).
[7] William Taft, Self-Defense and the Oil Platforms Decision, 29 Yale Law International Journal 295 (2004).
[8] See Daniel Bethlehem, Principles Relevant to the Scope of a State’s Right of Self-Defense against an Imminent or Actual Armed Attack by Non-State Actors, 106 Am. J. Int’l L. 1 (2012).
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