The Iran War, which began with Israeli and U.S. attacks on February 28, 2026, has not only threatened security in the Middle East and Europe but has also thrown the global economy into serious turmoil. The war has generated intense controversy regarding whether it can be justified under international norms and common sense. Furthermore, because NATO member states did not directly participate in the conflict, the war has also been viewed as exposing a crisis within the Atlantic alliance itself. British Prime Minister Keir Starmer initially refused to allow the use of British air bases for the first U.S. strikes against Iran on the grounds that the operation posed legal problems under international law. Only after Iranian retaliation resulted in attacks on U.S. forces did Britain invoke collective self-defense at the alliance level and agree to the use of British bases for defensive purposes. On March 2, Prime Minister Starmer explained before Parliament why he had denied the use of British bases during the initial strike phase, and his position subsequently became an important reference point for other NATO member states in determining their own responses to the war.1) Meanwhile, doubts regarding NATO cohesion deepened further after German Chancellor Friedrich Merz criticized the Trump administration for lacking a coherent strategy for the Iran War and argued that the United States as a whole was being humiliated by Iran,2) following which the U.S. Department of War announced the withdrawal of 5,000 U.S. troops stationed in Germany.3)

At the same time, the Trump administration proposed the “Maritime Freedom Construct” (MFC) in late April, arguing that freedom of navigation through the Strait of Hormuz must be guaranteed, and on May 4 announced a similar initiative known as the “Freedom Project.” However, NATO member states rejected President Trump’s proposal while maintaining the principle of non-involvement in the Iran War. Instead, they are currently pursuing a separate multinational framework aimed at guaranteeing freedom of navigation in the Strait of Hormuz only after the conflict is concluded either through a ceasefire or an indefinite suspension of hostilities. Whether the Iran War is regarded as lawful or not is therefore a core issue that will shape not only the level of support from U.S. allies and the broader international community, but also the long-term historical assessment of the war itself. After meeting Italian Prime Minister Giorgia Meloni on May 8, Secretary of State Marco Rubio complained to reporters that he did not understand why “nobody supports the Iran War.”4) This article argues that the war has failed to gain broad international support because it constitutes a preventive war that violates international norms and because the logic advanced to justify the strikes as preemptive self-defense remains weak. It also proposes policy recommendations for the ROK government regarding the United States’ requests for participation in the Maritime Freedom Construct and the Freedom Project.

Defensive War

Under international law, the type of war that can be justified without serious controversy is a purely defensive war conducted in the exercise of the right of self-defense. Because such a war conforms to international norms and is regarded as lawful, it is commonly described as a “war of necessity.” In general, this category includes wars clearly recognized as exercises of the right of self-defense under the United Nations Charter or wars authorized through a United Nations Security Council Resolution (UNSCR). Article 51 of the UN Charter defines the right of self-defense of member states as follows:5)

A representative example of a legitimate defensive war is the Korean War in 1950. Since there was clear evidence of North Korea’s full-scale invasion of South Korea, there was little doubt regarding the legitimacy of exercising the right of self-defense. Faced with the first major international conflict since its establishment, the United Nations adopted the following five Security Council resolutions, thereby creating both the legal justification and the institutional basis for international intervention in the Korean War. The fact that the United Nations Command (UNC) remains in existence even 76 years after its establishment reflects the strong legal foundation provided by the UN to repel an unmistakable act of aggression by North Korea.

The Gulf War, which began after Iraq’s invasion of Kuwait in 1990, also rested on a firm legal basis. Pursuant to UNSCR 678, adopted on 29 November 1990, a U.S.-led multinational coalition of 34 countries was formed to expel Iraqi forces from Kuwait. Likewise, the 2001 war in Afghanistan was widely regarded as a legitimate exercise of the United States’ right of self-defense because there was clear evidence that the Taliban regime, which provided sanctuary to al-Qaeda in Afghanistan, had enabled the September 11 terrorist attacks. The fact that NATO member states invoked Article 5 of the North Atlantic Treaty—the collective defense clause—for the first time in the alliance’s history further reinforced the legal legitimacy of the Afghanistan War. In contrast, in the case of the 2003 Iraq War, although the Bush administration attempted to secure a new UN Security Council resolution in order to strengthen the legal justification for military action, it failed to persuade other member states. The United States ultimately launched a preemptive attack based primarily on the unilateral claim that Iraq was developing weapons of mass destruction.

Preemptive War

Another type of war that may be permissible under international law is a “preemptive war,” in which a state that perceives an imminent threat attacks an adversary first. A preemptive war can also be regarded as a lawful and unavoidable war. However, the state that launches a preemptive strike must eventually present to the international community the reasons why striking first was unavoidable—that is, the specific nature of the threat posed by the adversary. Otherwise, it cannot avoid criticism that it merely disguised a preventive attack as a preemptive one. The 2003 Iraq War is a representative example. The Bush administration failed to provide concrete evidence supporting its claim that Iraq was developing weapons of mass destruction, which had been presented as the principal justification for the war. The conflict then dragged on for nine years. The United States was widely criticized, both domestically and internationally, for becoming trapped in a war without sufficient justification, and American society continues to suffer from the aftereffects of the Iraq War. The Iraq War also became an important catalyst for the emergence of the MAGA movement, which opposes overseas military interventions.

Preventive War

A preventive war, by contrast, is not permissible under international law. It refers to a war launched not because an actual threat already exists, but because a state assumes that a threat may emerge in the future and seeks to eliminate the possibility in advance. Such a war violates international norms and constitutes an unlawful war—a “war of choice” voluntarily initiated by the attacking unfriendly state itself. In reality, almost no country begins a war entirely without justification or explanation. Thus, purely preventive wars are rare. More commonly, wars initially presented as preemptive later come to be classified as preventive wars when the justifications offered prove unfounded and fail to secure international legitimacy.

Representative examples include Russia’s invasion of Ukraine in February 2022 and the U.S.-Israeli strikes against Iran in February 2026. Although low-intensity conflict between Russia and Ukraine had continued in the Donbas region, the prevailing international view was that there was no threat serious enough to justify Russia’s large-scale invasion. NATO and European Union member states have therefore regarded Russia’s actions as an illegal act of aggression posing a grave threat not only to Europe but also to international peace, and they have provided full support to Ukraine.

Likewise, the Trump administration failed to present sufficiently concrete and compelling evidence to justify the Iran War. As a result, unlike the 1991 Gulf War or the 2001 Afghanistan War, it did not receive broad support from the international community. Prominent international law scholars have even argued that the Iran War could constitute both a violation of the UN Charter and a war crime.6) Against this backdrop, NATO member states drew a clear line from the outset, insisting that the Iran War was not their war. Countries such as the United Kingdom, Spain, and Italy either opposed or imposed restrictions on the use of their bases and airspace by U.S. forces.

The Trump administration advanced two principal arguments to justify its preemptive strike against Iran: first, that an Iranian attack was imminent; and second, that Iran had not abandoned its ambition to acquire nuclear weapons. However, neither claim succeeded in persuading the international community because neither was supported by sufficiently credible evidence demonstrating a clear and imminent military threat to the United States.

(1) The Claim of an Imminent Iranian Attack

The argument that Iran was clearly preparing to attack the United States—and that the United States therefore faced an imminent threat requiring preemptive action—is evident in statements made by Secretary of State Marco Rubio and President Trump. On March 2, Secretary Rubio explained in a press briefing why a preemptive strike against Iran had supposedly been unavoidable. 7) The problem, however, was that he failed to present concrete and verifiable evidence capable of substantiating his assessment. As a result, the international community found little basis for accepting his argument.

The fact that President Trump’s decision was based on his own “feeling” that the Iranian threat was imminent became evident during the March 4 White House briefing by Press Secretary Karoline Leavitt.8) Leavitt argued that Trump’s feeling was grounded in facts, but she likewise failed to present objective evidence that could persuade the international community, offering instead only the President’s subjective judgment and personal belief.

Senator Mark Warner, the Democratic Vice Chair of the Senate Intelligence Committee, stated in a CNN interview on March 1 that there had been no imminent threat to the United States. He argued that the Iran War resulted not from any immediate danger, but entirely from President Trump’s own decision.9) Critics have also argued that Trump acted on instinct without listening to strategic advice, and that he was surrounded by aides who merely followed his decisions rather than presenting factual assessments.10)

(2) The Claim That Iran Never Abandoned Its Nuclear Ambitions

The second argument advanced by the Trump administration to justify the Iran War was that Iran had never abandoned its ambition to acquire nuclear weapons despite various agreements and international sanctions intended to halt its nuclear program. In his State of the Union address delivered on February 24, 2026, President Trump declared that Iran had not given up its “evil ambition” to possess nuclear weapons and vowed that the United States would prevent Iran from becoming a nuclear-armed state: 11)

President Trump also criticized Iran for refusing to abandon its nuclear ambitions and for reactivating its nuclear program in his national address announcing the outbreak of the Iran War.12) The White House additionally released dozens of past statements by President Trump, organized chronologically, in which he repeatedly declared his opposition to Iran acquiring nuclear weapons.13)

Iran’s nuclear development program described by Trump himself and senior administration officials have been “obliterated” immediately after the June 2025 airstrike under Operation Midnight Hammer.14) However, most experts are skeptical that Iran could have recovered sufficiently by February 28, 2026, to produce a nuclear weapon within a short period of time. Although the Trump administration claimed that Iran could build a nuclear weapon within weeks, the prevailing expert assessment is that the extensive destruction inflicted on Iran’s nuclear facilities would require far more time and effort for reconstruction.15) According to reports, the U.S. intelligence community assessed before the war that Iran was not actively developing nuclear weapons, and in the event of war it would likely attempt to block the Strait of Hormuz and attack U.S. forces stationed in the Gulf region.16) The U.S. intelligence community reportedly estimated before June 2025 that Iran would require approximately three to six months to produce enough fissile material for a single nuclear warhead, and revised that estimate to roughly nine to twelve months after the 2025 strike. Even after the outbreak of the Iran War in 2026, the assessment reportedly remained that Iran would still require up to one year to produce a nuclear weapon. 17) In addition, the U.S. Defense Intelligence Agency (DIA) assessed in May 2025 that Iran would likely not be capable of developing a long-range missile able to strike the U.S. mainland until around 2035.18) As with the claim that an Iranian attack on the United States was imminent, the assertion that Iran never abandoned its nuclear ambitions has failed to gain broad international support for the war because it relies not on concrete evidence or verifiable proof, but rather on the subjective judgments and assertions of Trump administration officials—assertions that also conflict with assessments from the scientific and intelligence communities.

Policy Implications

Thus far, the South Korean government appears to have responded to the Iran War in a rational and cautious manner. On the one hand, it moved swiftly both domestically and internationally to mitigate the economic shock. On the other hand, it approached the situation carefully and prudently in order to manage the ROK-U.S. alliance without becoming entangled in a war lacking broad international support. Just as Brussels declared that “the Iran War is not our war,” Seoul should continue to respond on the basis of the fundamental position that this is not Korea’s war.

The most pressing issue South Korea faces what role it should play in ensuring freedom of navigation through the Strait of Hormuz. This is also a highly sensitive matter closely watched by NATO member states. After President Trump specifically called on South Korea, China, Japan, the United Kingdom, and France on March 14 to participate in efforts to reopen the Strait of Hormuz, the G7 countries other than the United States, together with the Netherlands, issued a joint statement on March 19.19) The statement criticized Iran’s blockade of the Strait of Hormuz, emphasized the importance of maritime security and freedom of navigation, and declared that the signatories would play an appropriate role in ensuring safe passage. The essence of the statement was that countries not involved in the Iran War should cooperate—after the conflict has ended or tensions in the Strait have subsided—to ensure safe navigation, including through activities such as mine-clearing operations. At present, more than fifty countries, including South Korea, have joined this initiative, and summit meetings have been convened under British and French leadership while military-level preparations are also underway.

However, the Trump administration’s proposal in late April of the “Maritime Freedom Construct” and the “Freedom Project,” aimed at enforcing navigation through the Strait of Hormuz, has made the relationship between the U.S.-led initiative and the British-French-led international coalition an increasingly important issue. In particular, President Trump directly pressured South Korea for military participation on May 4 by citing an alleged Iranian attack on the South Korean cargo vessel Namu-ho.20) Within the South Korean government, some reportedly argue that Seoul cannot easily ignore Washington’s requests given the pending bilateral issues, and that accepting the proposal could help improve strained ROK-U.S. relations.21) Some also contend that South Korea should respond positively because the Namu-ho was attacked.

Nevertheless, considering the fact that the Iran War is widely viewed as a preventive war lacking international legitimacy, that the British-French-led international coalition in which South Korea is already participating explicitly excludes military intervention in the war itself, that Iran has stated it would regard countries participating in U.S.-led operations as belligerents, and that maintaining stable relations with Iran—which could emerge as a major regional power in the Middle East—remains strategically important, South Korean participation in the Freedom Project does not appear to serve the national interest. The preferable approach regarding the Namu-ho incident is to respond diplomatically once responsibility for the attack has been conclusively determined. Countries such as China, France, and Thailand, whose vessels were also attacked during the same period, have similarly limited their responses to diplomatic protests out of concern that stronger actions could lead to involvement in the Iran War.

Accordingly, the most desirable course for the South Korean government is to participate appropriately in the British- and French-led international cooperation framework. Even if South Korea were to dispatch naval vessels for mine-clearing operations or merchant ship protection, the risk of military confrontation with Iran would remain relatively low because such cooperation would be clearly distinguished from direct participation in the Iran War itself. Indeed, this type of international coalition could also serve as a form of diplomatic pressure on Iran and thereby contribute significantly to ensuring freedom of navigation. At the same time, it was undesirable that the government appeared confused and invited public distrust by initially downplaying the Namu-ho incident and responding in an overly passive manner. Given that war is currently underway in the Strait of Hormuz, the government must recognize the seriousness of the situation and mobilize a full-scale diplomatic response to ensure the safety of the twenty-six South Korean vessels currently operating in the region.

1. “The UK did not believe in regime change from the skies...., We all remember the mistakes of Iraq, and we have learned those lessons. Any UK actions must always have a lawful basis, and a viable thought-through plan.” Jessica Elgot and Dan Sabbagh, "Starmer says UK will not join ‘regime change from the skies’ on Iran," The Guardian, March 2, 2026.
2. Jim Tankersley, "Trump’s Clash With Merz Shows It’s Hard to Stay Friends With the President," New York Times, April 29, 2026.
3. Patrick Wintour, "Hope out of chaos: how the dark era of Trump is creating a new approach to global politics," The Guardian, May 2, 2026.
4. Crispian Balmer, "Rubio questions allies' support on Iran following Italy talks," Reuters, May 9, 2026.
5. https://www.un.org/en/about-us/un-charter/full-text
6. Tom Dannenbaum et al., "Over 100 International law experts warn: U.S. strikes on Iran violate UN Charter and may be war crimes," Just Security, April 13, 2026.
7. Secretary of State Marco Rubio Remarks to Press, Washington, D.C., March 2, 2026.
8. Press Briefing: Karoline Leavitt Holds a Press Briefing at The White House. March 4, 2026
9. Jacob Wendler, "Sen. Mark Warner says he saw 'no intelligence' of imminent threat from Iran," Politico, March 1, 2026.
10. Jeremy Bowe, "Trump is waging war based on instinct and it isn't working," BBC, March 29, 2026.
11. President Donald Trump's State of the Union address, delivered on Tuesday, Feb. 24, 2026, as transcribed by The Associated Press.
12. “Iran rejected every opportunity to renounce their nuclear ambitions, and we can't take it anymore. Instead, they attempted to rebuild their nuclear program and to continue developing long range missiles that can now threaten our very good friends and allies in Europe, our troops stationed overseas and could soon reach the American homeland.” "Fact-checking statements made by Trump to justify U.S. strikes on Iran," PBS News, February 28 2026.
13. “74 Times President Trump has made clear that Iran cannot have a nuclear weapon,” The White House Press Release, March 2, 2026.
14. Iran’s nuclear facilities have been obliterated — and suggestions otherwise are fake news, The White House Press Release, June 25, 2025.
15. Dan Vergano, "Iran was nowhere close to a nuclear bomb, experts say," Scientific American, March 11, 2026.
16. Alex Nitzberg, "US intel community agreed before war 'Iran wasn't developing a nuclear weapon': ex-counterterrorism chief," Fox News, May 8, 2026.
17. Gram Slattery, Jonathan Landay and Erin Banco, “Exlusive: US intelligence indicates limited new damage to Iran’s nuclear program, sources say,” Reuters, May 5, 2026.
18. "Fact-checking statements made by Trump to justify U.S. strikes on Iran," PBS News, February 28 2026.
19. Joint statement from the leaders of the United Kingdom, France, Germany, Italy, the Netherlands, Japan, Canada and others on the Strait of Hormuz, Press release, Government of the United Kingdom, March 19, 2026,
20. Lee Yu-mi, “Trump Pressures South Korea to Join Operations, Claiming ‘Iran Attacked a South Korean Cargo Vessel… It Is Time for South Korea to Join the Operation,’” Yonhap News Agency, May 5, 2026.
21. Lim Hyung-seop, “Blue House Deliberates Response Strategy for the Strait of Hormuz… Reviewing U.S. Request ‘in Consideration of Domestic Law,’” Yonhap News Agency, May 5, 2026; Yoon Da-bin, “Government Seriously Considering Participation in U.S.-Led Hormuz Coalition,” The Dong-A Ilbo, May 2, 2026.

※ The views expressed in this Sejong Focus are those of the author and do not necessarily reflect the official position of the Sejong Institute.