The Peninsula

Increasing the Value of the “Linchpin” Alliance Between the U.S. and South Korea

The alliance between the United States and South Korea faces one of its most consequential tests in seventy-two years. Some observers believe it may be nearing its breaking point, and there is growing concern in both capitals that the existing framework is no longer sufficient to meet the strategic demands of a far more dangerous world. If the alliance is to be placed on a steadier footing with the U.S. administration, it must be modernized and made fit for purpose for both sides—not only to deter threats on the Korean Peninsula but to uphold regional order and counter authoritarian aggression beyond it.

Some prominent U.S. conservatives view the Lee Jae Myung administration with deep skepticism, and President Donald Trump appeared to echo those doubts ahead of President Lee’s late-August visit. While their first summit was widely regarded as a success, Washington’s expectations are now significantly higher. Increasing defense spending, purchasing more U.S. weapons, and boosting host-nation support—steps that Seoul has already taken—may no longer suffice. The United States is now looking for its allies to contribute not just to their own defense but to the collective effort to maintain regional stability, deter China and North Korea, and defend the free world’s interests across the Indo-Pacific.

What other steps should the Lee administration consider? First, South Korea could engage in dialogue with the United States to identify ways the country can contribute to enhancing deterrence in the Taiwan Strait. Second, the two sides should explore options for leveraging South Korea’s defense industrial capacity to aid threatened countries in the Indo-Pacific and Euro-Atlantic, most notably the Philippines and Ukraine. And finally, as a reassurance step, the two sides could consider a joint statement reiterating their shared commitment to the alliance and to the presence of U.S. forces on the Korean Peninsula as a deterrent to North Korean, Chinese, and Russian aggression.

A History of Accomplishments to Be Proud Of

Before turning to a further discussion of how to advance the alliance, it is worth remembering that the alliance has been through difficult times before, including in the months surrounding the fall of Syngman Rhee and the coup by Park Chung-hee; after Richard Nixon’s 1972 visit to China; during the Koreagate scandal and the Jimmy Carter administration’s attempt to pull U.S. forces off the peninsula; in the wake of Chun Doo-hwan’s seizure of power; and after the tragic 2002 Yangju highway incident that resulted in the accidental death of two Korean schoolgirls, among others. The alliance came through these and other difficult moments because it undeniably and clearly delivers security, stability, resources for development, and opportunities for cooperation across a wide swathe of issue sets. And because without the alliance, both countries would be poorer, less respected in the world, and markedly less secure.

Since the signing of the U.S.-South Korea Mutual Defense Treaty in 1953, the alliance has served its primary function of keeping the Korean War from breaking out into open conflict again, providing space and support for South Korea to achieve extraordinary economic development and democratization and become a global cultural and technological powerhouse Indeed, the development of South Korea has proven hugely valuable for the United States; according to U.S. government statistics, South Korea’s foreign direct investment into the United States reached a cumulative USD 78.2 billion through 2023, supporting 88,100 American jobs and over USD 8 billion in U.S. exports; by contrast, the United States only invested USD 35.6 billion in South Korea. If South Korea were still poor, vulnerable, and living under martial law, rather than having developed into a wealthy and technologically sophisticated democracy through its partnership with the United States, it would likely be a recipient of aid and investment rather than a source of resources for U.S. growth.

Moreover, the investment of time, money, and lives made by generations of U.S. administrations, taxpayers, and servicemembers has been repaid by the achievements of the South Korean people not only through their development and democratization but also through the service of troops who served alongside the United States in overseas military operations. Americans who wonder about their allies’ willingness to contribute to upholding global order and security should know that South Korea deployed over 320,000 soldiers to Vietnam, with more than 5,000 killed and over 10,000 wounded. More recently, South Korea sent roughly 3,900 troops over two decades to support the international coalition in the war in Afghanistan. And in the conflict in Iraq, South Korea contributed the third-largest national contingent after the United States and the United Kingdom, rotating approximately 18,000 troops in total over the five years they were deployed. Such deployments relieved some of the burden on U.S. servicemembers and taxpayers, and reflect South Korea’s commitment to its alliance with the United States.

Contributing to Deterrence in Support of Taiwan

Despite these shared accomplishments, the allies cannot count on previous cooperation alone to carry their relationship forward. Leveraging its allies and partners for influence in the Indo-Pacific is particularly important for the United States in an era of growing geostrategic competition with China.

Secretary of State Marco Rubio, in his late July meeting with South Korean Minister of Foreign Affairs Cho Hyun, signaled that in addition to their “resolute commitment to the complete denuclearization of North Korea,” the two sides had reaffirmed the importance of peace and stability in the Taiwan Strait as an “indispensable element of security and prosperity for the international community” and the continuation of close U.S.-South Korea-Japan cooperation as embodied in the Spirit of Camp David.

Yet as some leading U.S. experts have noted, South Korea could do more, pointing out that it is untenable in the current environment to imagine that the United States would fight a nuclear-armed North Korea to defend South Korea but accept the country stand by and watch from the sidelines if the United States and its other Indo-Pacific allies were fighting a war against China in the Taiwan Strait. While it is unlikely that South Korea—or any U.S. ally—will respond positively to being publicly asked what they would commit to in a hypothetical Taiwan Strait contingency, it is not unreasonable to conduct such discussions behind closed doors and to expect South Korea to find some way to contribute.

Indeed, it is imperative that the parties quietly discuss in private what the United States would need from South Korea in a Taiwan contingency, how the South could assist, and what should be done in advance to help reinforce deterrence. Clearly, the primary role of the alliance is and should remain focused on deterring North Korea, which could seek to take advantage of any cross-strait conflict. But it would be a mistake for South Korea to think that it could avoid the consequences of a Chinese attack on Taiwan by staying neutral.

For its part, the Chinese People’s Liberation Army would likely target U.S. forces across the Indo-Pacific in the event of a conflict, meaning that U.S. Forces Korea, Combined Forces Command, and United Nations Command—as well as the installations and critical infrastructure supporting them all across the Korean Peninsula—would be under threat. South Korea, which survived North Korea’s June 1950 invasion only because the international community did not turn its back on the country at a key moment, should cast its lot in solidarity with its ally as it seeks to defend other nations threatened with existential annihilation by authoritarian revisionists, especially ones allied to and enabling North Korea.

A small but important first step that South Korea could take to help reinforce deterrence would be to formally join the Global Cooperation and Training Framework as a full partner, alongside the United States, Australia, Canada, and Japan, contributing its support to spread awareness of Taiwan’s experiences in key policy areas to benefit developing countries. Separately, given its dependence on maritime trade through the Taiwan Strait, it would be reasonable to ask South Korean naval vessels to conduct a transit of the strait, something U.S. and UK, Japanese, Canadian and Australian, New Zealand, German, French, and Dutch naval vessels have all done within the last year and a half. This might best be accomplished as part of, or on the way to and from, a joint military exercise with the U.S. Navy and another partner, such as Japan, the Philippines, or Australia. But such an operation could also be executed without being linked to travel associated with a multilateral exercise. Furthermore, the United States could provide an opportunity for South Korean representatives to engage with Taiwanese officials on the sidelines of a U.S.-hosted event at a venue such as the Daniel K. Inouye Asia-Pacific Center for Security Studies to share insights from its own experience with societal resilience that could help make Taiwan a harder target against Chinese pressure campaigns.

Contributing to the Arsenal of Democracies   

A second way South Korea can contribute to supporting the costs of maintaining the international order is by leveraging its defense industrial capacity to help democratic nations under threat through arms sales and transfers. South Korean defense firms can produce high-quality defense articles quickly and affordably, and have already demonstrated a willingness to endure Chinese complaints over such sales and transfers.

For example, companies like KAI and HD Hyundai have already sold light attack fighters and guided-missile frigates to the Philippines, providing key assistance to the modernization of Manila’s armed forces at a time when they are facing enormous pressure from China’s attempts to dominate and absorb most of the South China Sea. As of 2025, South Korea is Manila’s largest arms supplier, and the Armed Forces of the Philippines could likely benefit from additional capabilities in the form of air defenses and anti-ship missiles—opportunities for South Korea to export the Cheungong II medium-range surface-to-air missile or the K239 Chunmoo, together with associated targeting radar.

Separately, to date, South Korea has been unable to directly provide arms to Ukraine owing to legal restrictions that prevent the export of arms to conflict zones. Despite this, South Korea has landed on an approach that has seen it lend up to 500,000 155mm artillery shells to the United States, enabling it to backfill the U.S. military following munitions transfers to Ukraine. Now that South Korea’s domestic political deadlock has been resolved, and in light of North Korea’s direct support to Russia’s war effort, President Lee should use his near super-majority in the National Assembly to update and revise laws that constrain South Korea’s ability to export defense articles to any country deemed to be in South Korea’s interest to support, and then begin supporting Ukraine directly.

Making the Alliance Great Again Requires Enhanced Joint Commitment

To reassure the South Korean public and deter adversaries like North Korea, China, and Russia, the United States and South Korea should build on their statements reflecting an enduring commitment to the alliance. Secretary Rubio met with Minister Cho on September 10 in Washington, and the readout of their meeting said all the right things, underscoring “the lasting strength of the U.S.–ROK Alliance,” as well as the two sides’ intent to continue “advancing the U.S.-ROK Alliance through a forward-looking agenda that strengthens deterrence in the Indo-Pacific [and] expands equitable defense burden sharing.” For his part, Secretary of Defense Pete Hegseth stated at the Shangri-La Dialogue in Singapore in June that “America First certainly does not mean America alone,” noting that allies and partners will be instrumental in deterring China and North Korea.

More recently, on October 1, Minister Cho stated that, with respect to security cooperation, “an agreement has already been reached in general, which allows us to increase our national defence capabilities in necessary areas,” paving the way for deeper cooperation and enhanced South Korean contributions to the alliance. For her part, newly appointed Ambassador to the United States Kang Kyung-hwa described the alliance as having evolved over the past seven-plus decades into a “future-oriented comprehensive strategic alliance,” noting the Lee administration’s aim to “further strengthen this alliance.” Minister of National Defense Ahn Gyu-back has also signaled his confidence in the United States, dismissing speculation about troop withdrawals and indicating that the alliance will grow stronger and closer in the future.

As important and valuable as the U.S.-South Korea alliance is, it nonetheless requires leaders on both sides of the Pacific Ocean to take action to renew, revitalize, and reaffirm it. President Lee has entered office at a time when Washington is expecting new and more substantial contributions to global order maintenance, cost-sharing, and reciprocity from its allies. The days when the United States was willing to bear the lion’s share of maintaining peace and stability in the Indo-Pacific are in the past. There are tasks associated with deterring conflict and defeating aggression in the Indo-Pacific and the Euro-Atlantic that South Korea needs to contribute to, not as a favor to the United States, but as a partner who has benefited from the free world’s support for more than seven decades.

The U.S. presence in South Korea provides the U.S. government with options, influence, and significant cost savings compared to the disastrous implications of a renewed Korean War or a shift in South Korea’s overall geopolitical orientation. Advancing the relationship will require a partnership and frank, yet respectful, dialogue. As the past seven decades of the “linchpin” alliance have shown, it is certainly worth it.

 

Scott W. Harold is a senior political scientist at RAND, and a professor of policy analysis at the RAND School of Public Policy.

Feature image from 2nd Infantry Division/ROK-US Combined Division.

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