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Modernizing the ROK–U.S. Alliance: Key Implications and Challenges |
| August 14, 2025 |
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Bee Yun JoResearch Fellow, Sejong Institute | bjo87@sejong.org
- ‘Alliance modernization‘ has emerged as the foremost agenda item ahead of the first summit meeting between President Lee Jae-myung and President Trump in August 2025. Alliance modernization is being discussed as an umbrella concept encompassing the overall adjustments within the alliance in response to changes in the security environment and U.S. priorities as issues such as the transfer of wartime operational control (OPCON) under Trump’s second term, the strategic flexibility of U.S. Forces Korea, and defense cost-sharing have surfaced. This paper seeks to remind readers that within the ROK-U.S. alliance as well as in relations with other major U.S. allies such as Japan and NATO the term modernization is not frequently used. For the sake of ensuring the continuity of the ROK-U.S. alliance under Trump’s second term it is not advisable to outright reject the U.S. use of this term but finding an appropriate compromise point is deemed important. Regarding the role and scope of the alliance efforts should be made to develop based on official expressions used by both Seoul and Washington and to maintain and limit the expression modernization to the dimension of enhancing alliance capabilities. This paper is structured as follows. First, it highlights the changes in the official expressions regarding the use of the term modernization in the ROK-U.S. Security Consultative Meeting (SCM) joint statements and the roles and scope of the alliance and U.S. Forces Korea. It also provides an overview of the use of modernization in the official statements of the U.S.–Japan alliance and NATO thereby emphasizing the strategic weight of the term alliance modernization. Second, it identifies four issues that the debate on alliance modernization within the ROK-U.S. alliance may trigger. Third, it presents policy recommendations for the South Korean government.
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On August 8, 2025, U.S. Department of Defense spokesperson Kingsley Wilson reportedly stated that alliance modernization includes “adapting our combined (defense) posture to ensure credible deterrence on and beyond the Korean Peninsula, deepening interoperability, and expanding cooperation across all domains (land, sea, air, cyber, etc.).1)
While it appears to be a very comprehensive concept encompassing changes in the ROK–U.S. alliance under Trump’s second term, there is still no officially agreed concept or definition at the bilateral level. Moreover, looking back at previous transition periods in the ROK–U.S. alliance, modernization has not been a commonly used term at the bilateral level.
For example, even during the 2000s, which can be viewed as a major transition period for the ROK–U.S. alliance after the end of the Cold War, the concept of modernization appeared only once—at the 35th ROK–U.S. Security Consultative Meeting (SCM) Joint Statement of November 17, 2003. Against the backdrop of the U.S. Global Posture Review after 9/11, the two countries agreed on the Future of the Alliance Policy Initiative (FOTA) and, for its implementation, pursued relocation and realignment of U.S. Forces Korea, the transfer of military missions, and the enhancement of combined military capabilities. The 35th SCM specified that when these efforts were fully implemented, “the ROK–U.S. alliance will be modernized and strengthened and better able to adapt to the changing global security environment.” It should also be noted that the two sides “reaffirmed the continuing importance of the strategic flexibility of U.S. Forces Korea,” and that the term modernization at that time was used as a concept encompassing such adjustments and the strategic flexibility of U.S. Forces Korea.
Since then, the term modernization has not reappeared in SCM Joint Statements except for the 56th SCM last year. Instead, there has been progress in defining the role and contributions of the ROK–U.S. alliance beyond the Korean Peninsula. For example, the 50th SCM Joint Statement of October 31, 2018 emphasized “developing ROK–U.S. defense cooperation in a more mutually complementary and future-oriented manner, taking into account changes in the security environment,” and underscored the evolution toward a “comprehensive alliance.” The 53rd SCM Joint Statement of December 2, 2021 explicitly described the ROK–U.S. alliance as “the linchpin of peace and stability on the Korean Peninsula and in the Indo-Pacific region,” reaffirming that it would continue to develop “in a mutually complementary and future-oriented manner.” From the 54th SCM of November 3, 2022 onward, the two countries explicitly identified a “global comprehensive strategic alliance” as their shared vision and stated that they would continue to advance defense and security cooperation in the Indo-Pacific and international community “to respond more effectively to regional and global security challenges.”
The term 'modernization' reappeared in the 56th ROK–U.S. Security Consultative Meeting (SCM) Joint Statement of October 30, 2024. At that time, the two countries specified that, to develop the ROK–U.S. alliance into a global comprehensive strategic alliance, they would pursue “enhancing extended deterrence efforts against North Korea, modernizing alliance capabilities based on scientific and technological cooperation, and strengthening solidarity with like-minded countries and regional security cooperation.” However, this sentence indicates that 'modernization' at that time was focused on strengthening the alliance’s response capabilities to North Korea and enhancing alliance capabilities through the advancement of science and technology. In fact, since the 2020s, the two countries have emphasized security cooperation in emerging fields such as cyber, space, and artificial intelligence (AI), developing science and technology (S&T) cooperation into a core pillar of the alliance. Nevertheless, instead of using the term 'modernization' as in the 56th SCM, they have emphasized “cooperation in space and cyber” to improve “the alliance’s response capabilities.” The important point is that these discussions of 'modernization' have focused on “capabilities” rather than “threats.” This differs from the concept of 'modernization' in 2003, which encompassed strategic flexibility, or from spokesperson Wilson’s concept of 'modernization,' which emphasizes expanding the geographical scope of the alliance beyond the Korean Peninsula.
Another noteworthy point is the continued emphasis in past joint statements on the Korea-centered posture of the ROK–U.S. alliance and U.S. Forces Korea. While the two countries have responded to common security threats “in a future-oriented manner” and developed into a comprehensive or global comprehensive strategic alliance in accordance with changes in the security environment, they have clearly maintained the Korea-centered posture and purpose of U.S. Forces Korea. For example, in the 51st SCM Joint Statement, while confirming that U.S. Forces Korea plays an important role “in promoting peace and stability in Northeast Asia beyond the Korean Peninsula,” both sides also pledged to “maintain the current level of U.S. Forces Korea and improve combat readiness.” The ROK–U.S. alliance has repeatedly reaffirmed in its joint statements that “the Republic of Korea is defended under the terms of the ROK–U.S. Mutual Defense Treaty” (53rd SCM Joint Statement, December 2, 2021) and that U.S. Forces Korea has “played a central role in maintaining peace and stability on the Korean Peninsula for the past 68 years” and “will continue to play an important role in preventing armed conflict on the Korean Peninsula and promoting peace and stability in Northeast Asia.”
A general overview of the U.S.–Japan alliance and NATO shows that 'alliance modernization' does not address new geographical scopes. For example, the recent U.S.–Japan Foreign and Defense Ministers’ (2+2) Joint Statement stated that “the two countries will advance bilateral modernization initiatives to build a more capable, integrated, and agile alliance.” Here, 'modernization' focuses on strengthening interoperability, sharing capabilities, and improving mobility, with an emphasis on capability enhancement rather than geographical mission expansion. In the case of NATO, the 'modernization' concept is closely linked to “adaptation.” The “NATO 2030” agenda advocates “building a stronger NATO” and emphasizes institutional reform, establishing a resilient industrial base, and integrating new domains such as cyber and space. NATO’s 'modernization' discourse focuses on capability enhancement and cohesion, rather than expanding geographical reach as envisioned by the U.S. side of the current ROK–U.S. alliance. -
As examined above, the weight of the concept of 'alliance modernization' currently used by the ROK–U.S. alliance is by no means light and shows that a new transition period at the bilateral level is imminent. Spokesperson Wilson stated that the primary focus of the ROK–U.S. alliance remains “deterring North Korean aggression,” while also indicating that the United States “will continue to work closely with South Korea to link our shared priorities in the security environment beyond the Korean Peninsula.” This suggests that in the current debate on alliance modernization, adjustments to the role, objectives, and scope of the ROK–U.S. alliance in countering China will inevitably become a central issue.
In order to ensure the continuity of the ROK–U.S. alliance and maintain deterrence against North Korea under Trump’s second term, it is not advisable to directly reject the U.S. demands for 'alliance modernization,' but the debate on modernization of the geographic scope is expected to raise four key issues.
First, there is the possibility that the United States will urge South Korea to explicitly agree to the strategic flexibility of U.S. Forces Korea. On August 9, 2025, The Washington Post (WP) reported that during the ROK–U.S. negotiations, the U.S. was considering a plan for South Korea to issue a “political statement supporting the flexibility of U.S. Forces Korea’s posture for deterring China while continuing to deter North Korea.”2) Within the discussion on alliance modernization, the United States could demand that South Korea explicitly declare support for strategic flexibility.
Second, such explicit declarations regarding strategic flexibility could create a risk of 'overextension' of the ROK–U.S. alliance. As noted earlier, in ROK–U.S. documents 'modernization' has been focused on capabilities such as cooperation in new domains and science and technology. The more future alliance modernization shifts from such capabilities to threats and the expansion of geographical scope, the greater the risk of dispersing resources and political will away from the Korean Peninsula. Moreover, if the mission scope is broadened while the technical and institutional foundations of modernization are still incomplete, the alliance risks overextending itself before the groundwork is mature. This could undermine the credibility and effectiveness of the roles the ROK–U.S. alliance has pursued on the Korean Peninsula and in the Asia-Pacific/Indo-Pacific region.
Third, expanding the geographical mission places a significant burden on the command-and-control structure. If carried out alongside the transfer of wartime operational control (OPCON), it will demand more complex and sophisticated coordination and consultations, and without sufficient preparation and agreement, gaps could emerge in the alliance’s core mission of deterring North Korea under the ROK–U.S. Mutual Defense Treaty. Weakening deterrence against North Korea would directly affect the stability of the entire Indo-Pacific region, making radical or unilateral changes inadvisable. Fourth, another key concern is the potential deterioration of public opinion. If 'alliance modernization' were to shift rapidly from the defense of the Korean Peninsula to excessive delegation and burden-sharing across the Indo-Pacific region, it could provoke negative public sentiment in South Korea, which in turn could damage the alliance relationship. Such public opinion backlash is also likely to act as an obstacle to various initiatives the U.S. seeks to pursue in the future. -
Against this backdrop, this paper argues that the South Korean government should consider the following interconnected policy approaches. First, the emphasis of 'alliance modernization' should be reoriented toward alliance capabilities, technological advancement, and the deepening of deterrence. The focus should be readjusted to the discussions on "enhancing alliance response capabilities" and "cooperation" in new domains, which the ROK–U.S. SCM Joint Statements of the 2020s have utilized, and when necessary, South Korea should persuade the U.S. side to adopt the expression "modernizing alliance capabilities based on scientific and technological cooperation" (2024 SCM Joint Statement).
Second, regarding U.S. demands for countering China, these should be handled as a separate expression or category distinct from 'alliance modernization'. As noted earlier, since the late 2010s the two countries have declared in their joint statements that they would respond "in a future-oriented manner" to "changes in the security environment" and develop into a comprehensive or global comprehensive strategic alliance playing an "important role in promoting peace and stability" in the Asia-Pacific, Northeast Asia, or Indo-Pacific regions. The 55th SCM stated that the alliance would "deepen" and "expand" its regional engagement to jointly respond to regional threats and challenges. Meanwhile, regarding U.S. Forces Korea, both sides have continually reaffirmed the Korea-centered posture and purpose. Instead of explicitly using the terms 'strategic flexibility' or 'alliance modernization', finding a compromise within the continuity of existing terms and expressions used in past statements would strengthen sustainability and implementability for both sides as well as for domestic and international messaging.
Third, if more radical expressions or an explicit expansion of the geographical scope becomes unavoidable, it will be more important than ever to reaffirm that the primary mission of the ROK–U.S. alliance and U.S. Forces Korea remains the defense of the Korean Peninsula. If even this agreement on the primary mission proves difficult, the statements should explicitly list the defense of the Korean Peninsula first, followed by other areas.
Adjustments to U.S. Forces Korea in negotiations with the Trump administration are an unavoidable structural reality. Considering the potential development of North Korea–China–Russia relations and China’s military build-up in international waters near the Korean Peninsula, South Korea’s threat assessment of China also needs to be recalibrated. Furthermore, the tendency to limit the scope of the ROK–U.S. alliance solely to 'deterring North Korea' will not be accepted by the Trump administration. South Korea has now grown significantly in national power and military strength, to the point of being evaluated as fifth in the world in the conventional arms sector. 'Alliance modernization' is thus a turning point at which the ROK–U.S. alliance can move toward a more equal relationship and a chance for South Korea to strengthen its self-reliance, accelerate the transfer of wartime operational control (OPCON), and explore a policy shift under which South Korea takes the lead in responding to the North Korean threat.
Nonetheless, what this paper wishes to raise is whether the term 'alliance modernization' must be used. This is not to argue that the measures necessary for 'alliance modernization' should be avoided, but rather that in order to pursue this process in a more phased and gradual manner, South Korea should pay renewed attention to the expressions the two countries have gradually developed over time and, based on systematic threat assessments between them, seek to adjust and develop the alliance.
| ROK–U.S. Alliance and 'Alliance Modernization'
1) ” 연합뉴스. (2025. 8. 8.) 美 "동맹현대화, 한반도와 그 너머에 대한 억지력 확보 위한 것."
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2) The Washington Post. (2025. 8. 9.). “Trump expands use of tariffs to reach national security goals.”
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