U.S. Pressure to Form a Multinational Coalition in Hormuz and South Korea’s Policy Options

Executive Summary

Unable to break its stalemate with Iran following the expiration of the Islamabad Memorandum, the United States has shifted to a dual-pressure strategy combining military pressure with an economic blockade dubbed 'Operation Economic Outcast.' The EU is pursuing a two-track approach, officially joining the pressure campaign while minimizing direct military involvement; France has also refused to participate directly in operations to open the strait. Given that President Trump has publicly raised South Korea’s refusal to provide support in the Iran conflict, suggesting potential linkage to trade and defense cost-sharing negotiations, it would be advantageous for Seoul to secure rear-support options—such as dispatching a logistics support ship and maritime patrol aircraft, which the Blue House is reportedly considering—while delaying an announcement as long as possible. The most likely baseline scenario involves prolonged negotiations and the continuation of a nominal coalition. Therefore, rather than rushing a decision on deployment, South Korea should use its negotiating space to coordinate the form and level of its participation. This must be accompanied by a two-track response: reducing its dependence on energy supplies transiting through Iranian waters and engaging in preliminary diplomatic coordination to decouple the deployment issue from trade and defense cost-sharing negotiations.

I. Analysis of the Current Situation

Analysis of the Current Situation: U.S. Pressure to Form a Multinational Coalition in Hormuz

1. Background and Developments

The current crisis originated with the U.S.-Israeli airstrikes on Iran on February 28, 2026 [6][9]. Since the start of the war, the Strait of Hormuz has been under a de facto blockade [8][9]. Prior to the conflict, this waterway was the transit route for approximately one-fifth of the world's crude oil supply [6][9].

On June 17, President Trump and the government in Tehran signed a memorandum of understanding (MOU) known as the 'Islamabad Memorandum' [3][6]. It called for an immediate and permanent cessation of military actions on all fronts [9]. However, the Stockholm International Peace Research Institute (SIPRI) pointed out that the memorandum's provisions gave Iran scope to permanently restrict passage through the Strait of Hormuz [5]. The memorandum expired after 60 days, on August 17 [6].

After the memorandum expired, President Trump defined the Strait of Hormuz as 'U.S. territory' and effectively demanded Iran’s surrender [6]. Iran shifted its policy posture from defensive to offensive [6]. The situation then escalated, with the United States striking an Iranian launch site and Iran firing missiles at a U.S. military base in Jordan [18]. After more than six months of engagement, the two sides remain at a stalemate. Iran continues to keep the strait closed, while the United States maintains a naval blockade of Iranian ports [18].

2. Current Situation

During a trip that took him to Dubai, Jerusalem, and Palm Beach, President Trump announced that he was in discussions with seven countries about supporting efforts to secure the Strait of Hormuz [10]. This announcement came amid growing economic uncertainty due to high oil prices. While the U.S. administration stated it expected an early end to the war and a drop in oil prices, Iran countered that it is "stable and strong" and would maintain its defensive posture [10].

In parallel with military pressure, the United States has also deployed economic leverage. Secretary of the Treasury Scott Bessent announced 'Operation Economic Outcast,' vowing to cut the final economic lifeline supporting the Iranian regime and comparing the effort to the D-Day landings of World War II [2][13]. The Associated Press (AP) analyzed this as a pivot by the Trump administration to a dual-pressure strategy that combines the threat of military escalation with an economic blockade [13].

Ahead of the G20 summit, the European Union issued a statement officially confirming it would continue to pressure Iran alongside the United States, the G7, and international partners [1][15]. The EU stated that it 'welcomes efforts to compel Iran to cease its destabilizing activities and engage sincerely in peace negotiations, including through additional economic pressure such as Operation Economic Outcast' [1]. However, the Tehran Times reported that this move is facing growing internal criticism that the EU is gradually aligning with Washington's position, shifting from its initial stance that emphasized restraint and dialogue [7].

France had, in the initial stages, stated its refusal to participate directly in operations to open the strait. A senior official from the Blue House confirmed that the proposal for South Korea's military deployment was made jointly by the United Kingdom, France, and the United States, stating, 'From the time the UK, France, and the U.S. proposed an international coalition for freedom of navigation in the Strait of Hormuz, we have maintained that we would review the matter in consideration of our [military] readiness on the Korean Peninsula and our domestic legal procedures' [17].

Meanwhile, ahead of President Xi Jinping’s visit to the United States, President Trump unusually praised China for maintaining a 'relatively passive' stance throughout the Hormuz crisis [16]. This suggests that China was not an intended member of the multinational coalition the U.S. seeks to form, while also leaving room for interpretation as a conciliatory gesture ahead of the U.S.-China summit.

3. Key Actors and Positions

United Statesis pursuing a two-track strategy of simultaneously seeking to open the strait and pressure Iran. The Council on Foreign Relations (CFR) has projected that forming an international coalition will be a difficult task, given the Trump administration’s inherent skepticism toward alliances and multilateral institutions [8]. As a result, the CFR noted, the burden of guaranteeing freedom of navigation in the Gulf is likely to fall disproportionately on the United States [8].

European Unionhas publicly joined the broader cause of pressuring Iran, but appears to be justifying its participation by linking it to its own security interests, namely the protection of freedom of navigation. The EU has stated it is 'prepared to take further measures as necessary to protect its security and interests, including freedom of navigation' [15]. This can be read as rhetoric intended to frame its participation in the U.S.-led campaign not as simply following Washington’s lead, but as a decision based on its own interests.

Francehas a precedent of coordinating with economic pressure against Iran while drawing a line at direct participation in military operations to open the strait [see Summary]. This highlights the wariness within Europe regarding the risk of escalation.

Iranshifted to an offensive posture after the memorandum’s expiration, maintaining the closure of the strait as leverage [6][18]. Domestically, it is repeating the message that it is 'stable and strong' to showcase the regime’s defensive capabilities both at home and abroad [10].

Chinahas maintained a wait-and-see strategy throughout this crisis, avoiding a prominent role either militarily or diplomatically. President Trump’s public praise for this stance [16] indicates that the United States is fundamentally excluding Chinese involvement in the formation of the multinational coalition, while simultaneously using the issue as a tool for managing U.S.-China relations.

South Koreahas received a joint proposal from the United States, the United Kingdom, and France to participate in the international coalition for freedom of navigation [17]. The government is reportedly strongly considering the dispatch of a logistics support ship or a maritime patrol aircraft [11]. This is interpreted as a result of pressure from President Trump, who has repeatedly raised South Korea’s past refusal to provide support in the Iran conflict, suggesting that he could demand concessions on issues such as trade and defense cost-sharing [12].

4. Key Issues

The first issue is the dividing line between an 'alliance mission' and 'individual contributions.' A previous EAI report analyzed that when NATO convened a video conference on August 19, it found a middle ground between U.S. pressure for intervention and Europe's desire to avoid escalation by defining the effort not as an 'alliance mission' but as 'voluntary contributions from interested member states' [3]. This suggests a need for this distinction to be established in advance at the national level for individual countries, including South Korea [3].

The second issue is whether Iran's restriction on freedom of navigation is a temporary measure or whether it will solidify into a permanent status. SIPRI warned that the wording of the Islamabad Memorandum contained the potential to make Iran's navigation restrictions permanent in a final peace treaty [5]. In SIPRI’s judgment, this is an issue that could have repercussions for the principle of freedom of navigation worldwide, extending beyond the Gulf region [5].

The third issue is the internal policy conflict within the EU. A debate continues among EU member states over whether their participation in the pressure campaign against Iran is based on tangible security interests or is a political decision to align with Washington [7].

The fourth issue is the effectiveness of pressure on individual U.S. allies, including South Korea, to dispatch troops, and the associated domestic political burden. Cautious voices are being raised within South Korea, arguing that a decision on military deployment, which involves the lives of its citizens, cannot be rushed solely due to pressure from the United States [17].

II. In-Depth Analysis

In-Depth Analysis: U.S. Pressure to Form a Multinational Coalition in Hormuz

1. Analysis of Root Causes

At the root of the pressure to form a coalition is the practical limitation that the United States cannot guarantee the security of the Hormuz sea lanes alone. While noting the Trump administration's inherent skepticism toward alliances and multilateral institutions, the CFR assesses that the situation is structured such that the burden of securing freedom of navigation in the Gulf will inevitably fall disproportionately on the United States [8]. Although it was the United States that led the airstrikes on Iran and that maintains the naval blockade, the very fact that it has failed to reopen the strait after more than six months of engagement demonstrates the limits of a unilateral response [18].

President Trump's public pressure on South Korea, stating he would 'remember' its refusal to provide support in the Iran conflict, suggests that this limitation is translating into real domestic political frustration [12]. President Trump's remark that he 'received almost no help from other countries' in mine-clearing operations [13] shows that the attempt to form a coalition serves not only a military purpose but also carries a message of burden-sharing intended for a domestic audience.

Iran’s fundamental motivation is the opposite. As a previous EAI analysis pointed out, for Iran, control over the strait is 'not a bargaining chip, but an asymmetric lever directly linked to regime survival' [6]. For a country at an absolute disadvantage in conventional military power, blockading the strait is nearly the only means to offset the military superiority of the United States and Israel. Therefore, regardless of what multinational coalition might be formed, there is structurally no incentive for Iran to voluntarily relinquish control.

2. Structural Context

The Political Structure: The Flawed Islamabad Memorandum

The political backdrop for the current pressure to form a coalition is the failure of the Islamabad Memorandum, signed on June 17. SIPRI analyzed that a key provision of this memorandum was worded in a way that gave Iran scope to permanently restrict passage through the Strait of Hormuz [5]. Contrary to President Trump's declaration immediately after the signing—'Ships of the world, start your engines' [6][9]—the memorandum expired in just 60 days, and the strait reverted to a state of blockade. This reveals that the United States was unable to compel the reopening of the strait through military pressure alone from the start, and that the text of the agreement was itself the product of a political compromise that left advantageous loopholes for Iran.

The Economic Structure: The Combination of Dual Pressures

When its military pressure reached its limits, the United States shifted toward a strategy of combining it with an economic blockade. 'Operation Economic Outcast,' announced by Secretary of the Treasury Bessent, set the goal of cutting the final economic lifeline supporting the Iranian regime, an effort he compared to D-Day [2][13]. The AP characterized this as a pivot to a dual-pressure strategy combining the resumption of military escalation with a strengthened economic blockade [13]. Gulf News also reported that the United States is intensifying its economic blockade while maintaining the political frame that 'the conflict with Iran is not a war' [15]. This structure can be read as an attempt to raise the level of substantive pressure while minimizing the burden of finding a military justification.

The EU’s participation serves to grant international legitimacy to this economic structure. Ahead of the G20 summit, the EU issued a statement 'welcoming efforts to compel Iran to cease its destabilizing activities and engage sincerely in peace negotiations, including through additional economic pressure such as Operation Economic Outcast' [1][15]. However, the Tehran Times reported this as evidence of internal criticism that the EU is gradually aligning with Washington's position, shifting from its original policy that emphasized restraint and dialogue [7]. This criticism highlights the gap between the EU's traditional stance of maintaining an independent voice on Iran policy and its pragmatic choice to join the G7’s coordinated pressure campaign.

The Security Structure: The Institutionalization of Differentiated Alliance Responses

A previous EAI analysis noted that when NATO convened a video conference on August 19, it defined the effort not as an 'alliance mission' but as 'voluntary contributions from interested member states' [3]. This format sets a precedent for 'tolerating a differentiated response within the alliance system, where members directly exposed to threats, like Türkiye, respond actively, while most Western European countries limit themselves to minimal involvement' [3]. France's initial refusal to participate directly in operations to open the strait can be understood within this differentiated structure. France is pursuing a two-track approach: participating in the economic pressure campaign at the EU level while separately modulating its level of military involvement.

In South Korea’s case, this buffer mechanism is structurally absent. Because the ROK-U.S. relationship is a bilateral alliance, not a multilateral one, the NATO-style compromise formula of 'voluntary contributions' cannot be automatically applied. The statement by a senior Blue House official that 'From the time the UK, France, and the U.S. proposed an international coalition for freedom of navigation in the Strait of Hormuz, we have maintained that we would review the matter in consideration of our [military] readiness on the Korean Peninsula and our domestic legal procedures' [17] can be seen as an attempt to fill this structural void by citing the need to review domestic procedures. The JoongAng Ilbo has reported that the government is strongly considering dispatching a logistics support ship or a maritime patrol aircraft [11], which can be interpreted as a move to limit the scope of participation to the level of rear support rather than direct military intervention.

3. Comparison with Historical Precedents and Similar Cases

The current pressure to form a coalition bears a formal resemblance to past multinational escort operations in the Gulf region. The framework of a maritime security operation involving multiple nations to protect oil tankers is not new. What distinguishes this case from the past, however, is the fact that an official armistice agreement—the Islamabad Memorandum—was already in place, only to be effectively nullified in just 60 days [5][6]. This serves as an example that signing an agreement does not immediately guarantee the security of sea lanes, and it could reinforce skepticism about the effectiveness of early agreements in similar future crises originating in the Middle East.

Furthermore, the current dynamic—in which the EU has officially joined the pressure campaign against Iran while facing internal criticism for aligning with Washington [7]—stands in contrast to the independent diplomatic path the EU pursued regarding the Iran nuclear deal (JCPOA). At that time, the EU attempted to differentiate itself by opposing the unilateral U.S. reimposition of sanctions and exploring its own independent payment system. Its choice this time to officially join the U.S.-led economic pressure campaign demonstrates a significant shift in its policy stance toward Iran.

China's actions also offer a point of comparison. Ahead of President Xi Jinping’s visit to the United States, President Trump positively assessed China for being 'relatively inactive' during the Hormuz crisis [16]. This marks a departure from past patterns during periods of U.S.-China conflict, in which China would intervene in Middle Eastern affairs to gain leverage against the United States. China’s lack of significant intervention in the current crisis—beyond diversifying its crude oil supply sources—is likely a tactical show of restraint ahead of Xi's visit. Whether its policy stance will shift again after the crisis ends remains to be seen.

4. Key Variables Shaping Future Developments

The first variable is the sustainability of the EU’s internal cohesion. If the criticism of aligning with Washington, as reported by the Tehran Times [7], escalates into disagreements at the government level among EU member states, then even if the G7 joint statement holds, it is possible that fissures over the level of participation—similar to the case of France—could reappear during the practical implementation phase.

The second variable is whether the Trump administration’s dual-pressure strategy can actually induce a change in Iranian policy. While the strategy of combining an economic blockade with military strikes is already being implemented, as the AP has noted [13], the fact that Iran has not lifted the strait blockade even after shifting from a defensive to an offensive posture [6] raises questions about this strategy's effectiveness.

The third variable is the specific form of participation in the seven-nation negotiations. The nature of the burden that non-NATO allies, including South Korea, will have to bear depends on the level of contribution required by the seven-nation talks mentioned by President Trump[10] and whether this will follow a NATO-style framework of "voluntary contributions" or be institutionalized in a more binding form. The South Korean government's official acknowledgment that it is reviewing a dispatch of forces[17] while aiming for a limited contribution, such as a logistics support ship or patrol aircraft[11], can be interpreted as an attempt to preemptively set a minimum line of engagement amid this uncertainty.