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Earlier this month, President Donald Trump shared a Washington Post opinion piece on his social media, arguing that South Korea should send its Cheongung-II air-defense system to Ukraine. Additionally, the Trump administration continues to pressure Seoul to send troops to the Strait of Hormuz. Neither the U.S.-Iranian conflict nor the Russo-Ukrainian War is new, yet the simultaneity of U.S. pressure on Seoul to help in its war with Iran and to support Ukraine is striking.
While such diverging asks are indeed unprecedented, this is partly due to a lack of principles that stipulate a clear South Korean position. South Korea should establish a principle that requires multilateral legitimacy before it deploys its own troops overseas. It should also build a Lend-Lease-style legal framework, modeled on the World War II-era law, to govern arms sales to partners like Ukraine. In the absence of such principles, Seoul will continue to scramble each time an ally or partner calls, ultimately signaling its unpredictability and unreliability. As a member of the National Assembly who would cast one of the votes on any Hormuz deployment, I may soon be asked to vote for a decision Seoul is making without ever having settled the principle that should govern it.
A potential troop deployment to the Strait of Hormuz is complicated by independent equities Seoul holds in Iran. Seoul and Tehran built cultural ties dating to a 1969 Treaty of Friendship and a 1977 street-naming exchange, and economic ties that once sent more than 200,000 South Koreans to work in Iran’s infrastructure sector. As recently as 2017, Iran supplied 13.2 percent of South Korea’s oil imports, its third-largest source. That relationship still carries financial weight: From 2018 until 2023, South Korea held roughly $6 billion in frozen Iranian oil revenue, released only as part of a separate U.S.-Iranian prisoner swap.
Beijing and Moscow have stakes in these conflicts that far exceed Seoul’s own. China buys as much as 90 percent of Iran’s oil exports, making it far more exposed to any disruption in the Strait of Hormuz than South Korea is. China, South Korea’s largest trading partner, has also used economic retaliation in response to Seoul’s deployment of Terminal High Altitude Area Defense, a history that Seoul cannot ignore. Furthermore, Russia has issued a comparable warning directly to Seoul. When Seoul considered joining a NATO-led initiative to help purchase U.S. weapons for Ukraine, the Russian foreign ministry threatened “retaliatory measures, including ‘asymmetric’ ones.” Both powers have more at stake in these conflicts and more capacity to retaliate than South Korea does.
In the past, Seoul has deployed its troops to assist its ally, the United States, as well as in support of United Nations missions. For instance, Seoul sent roughly 320,000 troops to Vietnam, the largest foreign contingent after the United States, at the request of the United States. South Korea also deployed the Zaytun Division to Iraq from 2004 to 2008 as the third-largest contingent. Seoul also maintained the Akh unit in the Emirates, Dongmyeong with the U.N. force in Lebanon, and Hanbit in South Sudan. The record reflects a mixture of alliance assistance, non-combat roles when possible, and adherence to the National Assembly’s consent requirement. Nevertheless, Seoul needs a codified principle to govern its overseas troop deployment going forward.
Case in point: Seoul is having a premature public discussion of troop deployment only a few weeks after its annual joint military exercise with the United States was abruptly canceled and downsized. Are joint military operations fit for purpose when the very exercise meant to prepare that posture has just been cut? As Seoul’s internal debate over potential troop deployment is reported in the media, and the Defense Ministry confirmed it has sent a survey team to the Strait to assess conditions, the South Korean public is rightfully asking the same question. The South Korean president’s office has since ordered an audit to identify which agency leaked the internal deliberation, confirming that its own process lacks the discipline a governing principle would impose.
What further complicates matters for both American and South Korean policymakers is that any overseas troop deployment requires the consent of the National Assembly. In April 2003, the National Assembly approved sending non-combat engineering and medical units to Iraq. The more consequential vote came in Feb. 2004. It approved a separate and far larger deployment, a roughly 3,000-troop Zaytun Division. Seoul structured Zaytun under its own independent command, designated primarily for peacekeeping. The unit is named “Zaytun,” Arabic for “olive,” as a symbol of peace. The deployment rested on U.N. Security Council resolutions 1511 and 1546 — legal backing that the current case for Iran lacks.
The first Trump administration’s crisis with Iran heightened in the aftermath of the Fujairah attacks, the Saudi Aramco strike, and the Qassem Soleimani killing. In response, Seoul chose to expand its forward-deployed Cheonghae unit into the Gulf of Oman and the Persian Gulf without joining the U.S.-proposed International Maritime Security Construct. It was a compromise made to assist the United States in protecting sea routes for shipping and energy imports and maintaining a long-term relationship with Iran. Yet, Seoul expanded the Cheonghae unit’s area of operation to bypass the National Assembly’s consent, drawing widespread criticism from lawmakers. It was based on a clause governing the Cheonghae unit’s deployment, which allows its operating area to expand to protect South Korean citizens during a crisis.
While the 2020 approach was an attempt to maintain ambiguity in complicated geopolitics, such an episode cannot be repeated during a hot war situation in the Strait of Hormuz today. Initial media coverage included, and the Ministry of Defense has yet to confirm, potential assets such as P-8A Poseidon maritime patrol aircraft, a naval explosive ordnance disposal team, and a logistics support ship, with missions running to surveillance to mine clearing. Even so, the government and ruling party admit that such a mission requires the National Assembly’s consent regardless of its non-combat nature. What further complicates matters is the ruling party’s ambivalence about the mission’s clarity and necessity, leaving it uncertain whether the government can secure enough votes for the required consent.
According to a Sept. 7 survey of 1,020 South Koreans by the Reform Institute, a think tank affiliated with the opposition Reform Party that the lead author led until last month, 62.4 percent called the U.S. request for a Hormuz deployment unjustified. The same survey found that 61.3 percent said the government mishandled bringing the question into public view. Independent, nonpartisan polling from the same week points in the same direction: A joint survey by four independent polling firms found 45 percent opposed to a Hormuz deployment against 36 percent in favor, while an additional independent poll found the public split within the margin of error: 47.1 percent opposed to 43 percent in favor. None of this describes a public eager for Seoul to get involved.
The Reform Institute poll also found that, when forced to prioritize, 41.4 percent wanted neither a Hormuz deployment nor Ukraine arms support, a larger share than either option drew on its own. The honest finding is not that South Koreans favor coalition participation outright. Among those willing to entertain any involvement at all, however, coalition-only participation is the clear preference, chosen by 37.6 percent overall and by 61.9 percent of even those who called the American request unjustified when the alternative was doing nothing. Additionally, the Reform Institute’s poll found that 84 percent said prior reporting to and deliberation by the National Assembly should come before any decision.
Foreign policy and national security are often treated as insulated from domestic politics, but the salience of the tariff issue shows that insulation no longer fully holds. The poll results above therefore carry real weight for the principles this piece proposes. The first principle should address when Seoul would provide armed support in an active conflict zone such as the Strait of Hormuz, a decision complicated by the waterway’s importance to South Korea, which receives nearly two-thirds of its oil and one-fifth of its liquefied natural gas imports through it. The United States and South Korea have a formal mutual defense treaty, but that treaty does not address a conflict initiated by either ally or a conflict outside of either party’s administrative control — it applies only to the narrower scenario in which one of the two is attacked.
Any South Korean troop deployment in the Strait of Hormuz should require multilateral legitimacy — either a recognized coalition or a comparable basis in international law, rather than an ad hoc, standalone deployment. Pyongyang has spent the past two years deepening its military partnership with Moscow. It has sent its own forces to fight in Russia’s war against Ukraine, reportedly in exchange for technology transfers that sharpen its missile and reconnaissance capabilities. South Korea’s own readiness exercises have just been scaled back. Facing a more capable and now internationally entangled adversary at home, the South Korean military has good reason to keep the capacity it has concentrated on the Korean Peninsula rather than dispersing it to the Persian Gulf. This is not an argument against any contribution at all: Multilateral legitimacy, unlike a standalone deployment, can supply capabilities and political legitimacy Seoul cannot generate on its own.
This legitimacy can take one of two forms. The first is a recognized coalition, a formally announced multinational effort with a public mission statement and named participants. The second is a comparable basis in international law, which can include a U.N. Security Council resolution, a standing U.N. peacekeeping mandate, or an invocation of the customary right to protect freedom of navigation. What matters is that one of these bases exists, not the operational command structure Seoul then chooses. For instance, the Zaytun Division operated under Seoul’s own independent command despite resting on a Security Council resolution, and Dongmyeong operates fully integrated within the U.N. Interim Force in Lebanon’s standing peacekeeping mandate, both qualifying under the second basis regardless of command structure.
The International Maritime Security Construct, assembled by the United States in 2019 without U.N. authorization, is the most instructive case. It shows the second basis can be met through the customary right to freedom of navigation alone, and that meeting the standard does not obligate Seoul to participate. When the construct was announced, Seoul expanded its own Cheonghae unit’s operating area rather than formally joining it. What would not qualify is a deployment, like the one now under discussion, that lacks any comparable multilateral backing of either kind.
This standard benefits both the United States and South Korea in the case of Hormuz and in future conflict scenarios, since it provides Washington with levels of support that no single country can offer, and it minimizes the risk that any one country takes on to support its allies. If Washington prefers a faster bilateral arrangement and declines to assemble a coalition, Seoul should hold the line rather than abandon the principle under pressure. The resulting friction is a real cost to the alliance, but a lower one than the risk a unilateral deployment would create. Additionally, a South Korean deployment lacks logistical feasibility. The destroyer currently rotating through the Cheonghae mission in the Gulf of Aden is configured for anti-piracy rather than for the drone and mine threat in the Strait. Transit from Korean waters takes roughly a month, and detaching hulls thins coverage at home at exactly the moment the Korean Peninsula needs them.
The second principle needs to clarify to whom Seoul exports its state-of-the-art defense products, and when. Immediate export of Cheongung-II (KM-SAM Block II) to Ukraine is limited for two reasons: a longstanding South Korean policy against exporting arms to parties in active conflict, and a supply shortage tied to existing contracts and commitments. South Korean defense exporters need a Defense Acquisition Program Administration permit, which can be restricted under the Defense Acquisition Program Act’s enforcement decree for reasons including war. Also, the Foreign Trade Act separately limits permits to goods used “for peaceful purposes.” However, both restrictions fall within the enforcement decree or ministerial notice level rather than the statutes themselves. It means that the government can tighten or loosen them by cabinet or ministerial decision alone, without a National Assembly vote. In the past, South Korea has supplied 155-millimeter artillery ammunition to the United States rather than to Ukraine, to not violate that policy.
Also, there is a significant institutional gap in overseas arms sales between Seoul and Washington. Unlike America’s Foreign Military Sales program, which operates under congressional oversight, arms exports from South Korea are authorized administratively by the Defense Acquisition Program Administration, an agency under the Ministry of National Defense. Under the U.S. Arms Export Control Act, foreign military sales above a set dollar threshold should be formally notified to Congress, with fixed windows to block the transfer by joint resolution before it can proceed. No equivalent check exists in South Korea: A hypothetical Cheongung-II sale to Ukraine would be authorized entirely within the Defense Acquisition Program Administration and the Ministry of National Defense, while the National Assembly holds no formal role, no notification requirement, and no statutory window to object.
One way to close this gap is a statutory notification-and-objection window: The Defense Acquisition Program Administration would retain authority to approve or deny exports, but transfers above a certain threshold or to active conflict zones would require formal notice to the National Assembly of either decision, with a fixed period during which it could block an approved sale or compel review of a denied one.
In addition, the 1941 Lend-Lease Act offers some room for emulation. As the act authorized aid to any country “whose defense the President deems vital to the defense of the United States,” South Korea needs its own statutory criteria: aid tied to a partner’s centrality to the rules-based order or to the supply-chain stability South Korea depends on, rather than treating each transfer as a political decision every time.
A similar nonbelligerency firewall that lets the United States arm Britain and other nations without becoming a co-belligerent could give South Korea’s existing policy more flexibility in supporting Ukraine. It is true that the nonbelligerency firewall did not hold for the United States in the end. Also, the Ukraine Democracy Defense Lend-Lease Act, which passed the U.S. Congress in 2022, went unused. Nevertheless, Seoul can begin to establish a statutory framework for predictability. It is worth noting that the Lend-Lease also required the U.S. president to report regularly to Congress on what aid went to which recipient, a workable template for the National Assembly notification mechanism the institutional gap above calls for.
South Korea’s defense industry has grown significantly over the past decade and is projected to keep growing. Yet the defense industry is unique in that its exports are inherently entangled with the country’s foreign policy and national security. While many in Seoul have welcomed this growth and its economic benefits, the government now needs to clarify a principle for arms exports that advances and protects South Korea’s vital national interests without making it a co-belligerent in active conflicts.
The Trump administration’s continuing demands for troop deployment in the Strait of Hormuz and arms exports to Ukraine have stirred bilateral relations, further complicated by a trade and tariff deal many in the South Korean public consider inherently unfair. Nevertheless, one silver lining is the growing recognition that South Korea needs clear principles: a standard requiring multilateral legitimacy for troop deployment in support of allies and partners, and a statutory framework governing arms sales to countries in peacetime and war. Hormuz and Ukraine are the most immediate questions Seoul’s policymakers face today, but they will not be the last. Only a clear strategy will make South Korea a reliable ally and partner.
Jun-seok Lee is a member of the National Assembly of the Republic of Korea. He previously served as the youngest-ever leader of the People Power Party, later led the Reform Party until Aug. 2026, and was a 2025 presidential candidate. He is a member of the Korea-U.S. Parliamentarians’ Union and a frequent contributor to bilateral policy discourse.
Donghyeon Kim is Rep. Lee’s national security advisor.
Image: Cristian Schrik via DVIDS
