The Future of the ROK-U.S. Alliance: Adapting to a Changing World

Newsletter by Kyeongdoo Jeong

Published September 30, 2025

For more than seven decades, the ROK-U.S. alliance has stood as an ironclad partnership, shaping not only the security of the Korean Peninsula but also the broader trajectory of the Republic of Korea (ROK)'s national development. Today, however, the question of how to modernize this alliance has come to the forefront. The reason lies in the shifting security environment of the international community, which now demands a reassessment of old assumptions and fresh thinking about future cooperation.

This piece reflects on the legacy of the alliance, examines how global and regional changes affect its future, and outlines the most desirable path forward for the ROK-U.S. partnership.

The Establishment and Development of the U.S.-ROK Alliance
After the Korean War in 1953, the ROK-U.S. Mutual Defense Treaty was concluded to deter war and prevent communist influence on the Korean Peninsula, and it began as a military security alliance. Since then, it has successfully carried out the mission of deterring the outbreak of war on the Korean Peninsula and maintaining peace in Northeast Asia and has realized the common values of the two nations, such as freedom, democracy, peace, welfare, and prosperity.

The ROK-U.S. alliance has also left a profound mark on South Korea's national development in several key ways.

First, through the deterrence of war on the Korean Peninsula, it has played the role of a key axis guaranteeing not only the security of the Korean Peninsula but also peace and stability in Northeast Asia.

Second, with the prosperity of the free-market economy system, South Korea, which had a per capita income of $67 in 1953, emerged as an advanced economic power in 2024 with a per capita income of $36,624.

Third, it achieved political democratization, became a country that respects the universal values of freedom, democracy, and human rights of the international community, and became a member of the Organisation for Economic Co-operation and Development.

Fourth, its diplomatic status in the international community was also enhanced, as it currently has diplomatic relations with 194 countriesand has transformed from an aid recipient to a donor.

Fifth, it has developed into a global comprehensive strategic alliance, starting from a military security alliance and expanding into the fields of economy, science and technology, culture, health care, space, and cybersecurity. The ROK-U.S. alliance has also greatly contributed to the development of the national defense of the Republic of Korea. According to the Global FirePower, the Republic of Korea has risen to a military power ranked fifth in the world.

When introducing advanced weapons, it applied the offset procedure and transferred technology for trainer and fighter aircraft development. Through the establishment of the ROK Air Force Operations Command, it has established the world's strongest operational capabilities as well as a systematic defense management system, including planning, personnel, and logistics.

There are many other positive achievements, and the Republic of Korea is evaluated as the most exemplary case among the countries supported by the United States. Therefore, I am convinced that the Republic of Korea is a nation that has become a source of pride for the United States, its ally.

Shifts in the International Security Environment
First, South Korea's geopolitical security environment presents a series of distinct challenges.

North Korea continues to press ahead with its nuclear and missile programs while also posing threats in cyberspace and through ambiguous forms of terrorism. Its deepening military ties with Russia have further sharpened bloc-to-bloc confrontation, and with Pyongyang having erased the very concept of unification from its political vocabulary, the prospects for renewed dialogue remain bleak.

China may be South Korea's largest trading partner, but it continues to back North Korea and contribute to an increasingly unstable international order. Beijing has sought to expand its military footprint, including through the construction of structures in the Yellow Sea, while maintaining a heavy-handed posture toward Seoul's diplomacy. It repeatedly presses Korea to move away from a U.S.-aligned foreign policy and insists that the so-called "Three No's" policy on Terminal High Altitude Area Defense (THAAD) remains immutable.

Russia designatedSouth Korea as an "unfriendly"nationbecause it participated in sanctions against Russia for the Ukraine War. With North Korea's dispatch of troops to the Ukraine War as an opportunity, it strengthened the relationship by concluding a North Korea-Russia treaty. The Putin regime has been solidified, and the new Cold War structure is highly likely to be prolonged.

With Japan, historical disputes and territorial ambitions continue to cast a shadow over relations. Yet given the strength of the U.S.-Japan alliance, building a future-oriented framework for ROK-U.S.-Japan cooperation is more important than ever.

Second, shifts in the broader international security environment are reshaping the strategic landscape.

China's rise has sharply intensified its rivalry with the United States, turning their competition for hegemony into open conflict. Guided by the vision of the "China Dream" (中國夢), Beijing openly aspires to overtake the United States by 2049 and claim global leadership. Its economic growth has been striking, from just 12 percent of U.S. GDP in 2000 to 40 percent in 2010, 70 percent in 2020, and an estimated 85 percent by 2025. Washington attempted to "decouple" in order to reduce economic dependence on China, but the two economies are too deeply intertwined, particularly in manufacturing and trade. As a result, U.S. strategy has shifted toward "derisking"-curbing the leakage of advanced technologies while managing the realities of economic interdependence.

China weaponized rare earth resources, which account for about 60 percent of global reserves, and has confronted the United States directly by declaring anti-dumping duties of 33.3 percent to 78 percent on U.S. specialty optical fibers on the day of its 80th Victory Day "military show."

Militarily, China has long viewed its humiliations at the hands of Western powers from the mid-nineteenth century to the end of World War II as the result of weak sea power, and it has been determined to correct that ever since. In 1982, Beijing adopted its anti-access/area denial (A2AD) strategy, anchored by the establishment of the first island chain. Today, China underscores the "One China" principle on issues of Senkaku sovereignty and Taiwan, presses its maritime claims by constructing 12 artificial islands in the South China Sea and building structures in Korea's Yellow Sea, and in 2022, it signed a security cooperation pact with the Solomon Islands-an unmistakable sign of its expansion into the Pacific. By 2040, China aims to break through the second island chain, steadily extending its maritime reach.

Alongside these trends, a new Cold War dynamic has taken shape, pitting the ROK-U.S.-Japan trilateral against a North Korea-China-Russia bloc. At the same time, the rapid advance of science and technology has amplified non-traditional security threats-from space and cyber to climate change, pandemics, terrorism, and natural disasters-that no nation can manage alone. Confronting these challenges will require greater solidarity and cooperation within the international community.

Major Security Issues of the ROK-U.S. Alliance Arising from Shifts in the International Security Environment
First, regarding the strategic flexibility of U.S. Forces Korea, there is the issue of expanding participation in the Indo-Pacific strategy and strengthening ROK-U.S.-Japan security cooperation. The main content is that the ROK military responds proactively to North Korean threats, while U.S. Forces Korea is expanded and adjusted to deter China in the Indo-Pacific region.

Second, there is a demand to increase the ROK defense budget. It is required that the ROK defense budget be increasedto 3.5percentto 3.8percentof GDP(currently at the 2.3 percent level).

Third, there is a demand to increase the defense cost-sharing of U.S. Forces Korea. It is requested to increase it to the level of $10 billion(currently at the $1.1-1.2 billion level).

Fourth, there is the issue of the transition of wartime operational control. Since 2006, during the process of transitioning operational control, negative opinions have been expressed, such as the withdrawal of U.S. Forces Korea, the dissolution of the UN Command, and the reorganization of the combined command system.

Desirable Future for the ROK-U.S. Alliance
Calls to modernize the ROK-U.S. alliance can be partially accommodated. Given the strength of South Korea's armed forces, Seoul is well-positioned to maintain overwhelming superiority against North Korea's conventional threats. If the role of U.S. Forces Korea is broadened to deter China in line with the shifting international security environment, it will be essential to ensure that security tensions in Northeast Asia do not spiral upward and that no gap emerges in responding to Pyongyang's provocations. For this reason, Washington should make an explicit commitment to its extended deterrence-the nuclear umbrella-while preserving a degree of strategic ambiguity when it comes to flexibility in force posture.

Demands for a larger ROK defense budget can also be partially met. With South Korea's military already ranked fifth in the world, it is unrealistic to hold Seoul to the same spending benchmarks as other countries. Still, budget increases can serve as an opportunity to bolster advanced capabilities needed to counter emerging threats with confidence. At the same time, Washington should do its part by approving the export of advanced weapons and extending technological support to its ally.

The debate over defense cost-sharing should be resolved through a clear understanding of the facts and a rational negotiation process. South Korea is already a model contributor to the upkeep of U.S. Forces Korea. Beyond direct financial support, Seoul also bears significant indirect costs-such as land and facility use, tax exemptions, and weapons purchases-that deserve recognition. By making these efforts more visible and by finding ways to reduce the rigidity of current budget structures, which are heavily tied to labor, construction, and logistics, both sides could achieve more practical and effective outcomes.

The transition of wartime operational control should proceed under the existing plan, with strict adherence to agreed procedures and minimal political interference. As outlined in prior ROK-U.S. agreements, the transfer must be conditioned on specific benchmarks being met. Even after the handover, U.S. Forces Korea should remain on the Korean peninsula to fulfill Washington's defense commitments, while the UN Command-long a stabilizing force in deterring armed conflict-continues to operate and receive support. At the same time, institutional ties among the ROK Joint Chiefs of Staff, the Combined Forces Command, U.S. Forces Korea, and the UN Command should be further developed. This arrangement would allow South Korea to steadily expand its capacity to lead combined defense while the United States continues to provide complementary and sustaining capabilities, including the assurance of extended deterrence against external aggression.

Beyond traditional defense, the alliance must also expand its concept of security to reflect new realities. South Korea's strengths in strategic science, technology, and advanced manufacturing offer powerful tools to deepen the ROK-U.S. partnership while fueling economic growth for both nations. Initiatives such as the shipbuilding cooperation program (MASGA project), along with Korea's competitive edge in semiconductors, secondary batteries, nuclear power plants, and the defense industry, should be leveraged to reinforce the alliance. At the same time, Seoul and Washington should continue to build a cooperative, mutually beneficial framework to confront emerging threats in cyber, space, terrorism, and disaster response.

Conclusion
The ROK-U.S. alliance, which has developed into the most powerful alliance in the world over the past 72 years, can continue to develop as the most exemplary alliance in the world if the spirit of "respect" and "consideration" is maintained.

Kyeongdoo Jeong was the 46th Minister of National Defense for the Republic of Korea from 2018 to 2020.

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