1. The Debate on Modernizing the ROK-U.S. Alliance

Since the 21st century, the security environment in the Indo-Pacific region has undergone fundamental changes. China's economic rise and military modernization, North Korea's advancement of its nuclear capabilities, and the intensifying U.S.-China strategic competition pose structural challenges to the existing regional security order. Within this altered security landscape, the traditional bilateral alliance structure demands adaptation and innovation to effectively respond to new threats. Alliance modernization centers on improving and strengthening existing alliance frameworks to more effectively address the changing security environment and new challenges. In this context, discussions on modernizing the ROK-U.S. alliance set as a core direction the expansion of the alliance's operational scope and strategic role from a Korea-centric system to the Indo-Pacific region, in response to the evolving regional security environment. This signifies not merely a quantitative expansion of the existing alliance relationship, but a qualitative transformation of the alliance's strategic horizon and operational domain. Specifically, ROK-U.S. alliance modernization encompasses the following key areas (Min Jeong-hoon 2025). First, securing strategic flexibility through adjustments to the size and role of US Forces Korea. Second, expanding the ROK military's primary role in the defense posture against North Korea and the corresponding increase in defense spending. Third, establishing a joint response system for military threats beyond the Korean Peninsula within the region.

The prevailing analysis holds that the core of the alliance modernization pursued by the United States lies in securing strategic flexibility for US Forces Korea (USFK) to counter China. This implies that USFK must transition from its traditional role of defending the Korean Peninsula to a system capable of performing broader regional security missions. Perceptions and evaluations of ROK-US alliance modernization among South Korea's political elites show significant differences depending on political affiliation (Yang Ji-ho 2025). The conservative camp maintains that strategic flexibility for containing China must be accepted within the framework of the ROK-US alliance. Citing Article III of the ROK-US Mutual Defense Treaty, they argue that if the US is attacked in the Indo-Pacific region, South Korea could be automatically drawn into the conflict. They contend that the very presence of USFK on the Korean Peninsula serves not only as a deterrent against North Korea but also as a means to contain neighboring countries. Conversely, the progressive camp maintains that the ROK-US alliance is fundamentally centered on the Korean Peninsula. They judge that the purpose of USFK's presence is to provide war deterrence and defense capabilities against attacks from North Korea, expressing the view that it is difficult to accept strategic flexibility for USFK deployed for North Korean deterrence.

The security strategy of the second Trump administration, which prioritizes containing China, suggests potential changes to the size and role of U.S. Forces Korea (USFK). Under the new strategic vision, USFK is expected to shift toward concentrating its capabilities on containing China, while anticipating that South Korea will take a more proactive role in responding to the North Korean threat (Yang Wook and Lee Kyung-seok 2025). In this context, The Wall Street Journal published an article raising the possibility of reducing the 4,500-strong Stryker Brigade currently deployed on a rotational basis in South Korea (Youssef, Ward, and Martin 2025). Within Washington, arguments have even surfaced advocating for a significant reduction in USFK troop levels to approximately 10,000 (Kavanagh and Caldwell 2025).

As the modernization of the ROK-U.S. alliance emerges as a core agenda item for both Korea and the United States, systematically analyzing the perceptions and attitudes of the Korean public toward these changes holds significant policy implications. The democratic legitimacy and sustainability of alliance policy must be grounded in national consensus and support, which requires accurate measurement and analysis of public opinion. This report comprehensively analyzes Koreans' perceptions regarding changes to the role of U.S. Forces Korea (USFK), utilizing the latest public opinion poll data conducted by the East Asia Institute (EAI) in August 2025. By identifying key factors driving shifts in perception, it aims to derive strategies for building public consensus on modernizing the ROK-U.S. alliance and policy implications, thereby contributing to exploring a more stable and sustainable direction for alliance development.

2. Koreans' Perceptions of Changes in the Role of U.S. Forces in Korea and the ROK-U.S. Alliance

Since the signing of the Mutual Defense Treaty between Korea and the United States in 1953, the core mission of U.S. Forces Korea (USFK), stationed in South Korea, has been deterrence against North Korea—defending South Korea from North Korea's military threats. This traditional role has formed the bedrock of the ROK-U.S. alliance for over 70 years and has functioned as a central pillar of the Korean Peninsula's security architecture. However, as discussed earlier, amid the changing security environment in the Indo-Pacific region, discussions on alliance modernization persist in Washington, arguing that the existing mission of USFK should be expanded from deterrence against North Korea to containment of China. What perceptions do South Korean citizens hold regarding this potential policy shift? The results of a public opinion poll conducted by the East Asia Institute (EAI) in August 2025 offer intriguing insights.

[Figure 1]: South Koreans' Perceptions of the Changing Role of U.S. Forces in Korea

As shown in [Figure 1], 58.5% of South Korean citizens expressed approval regarding the change in the role of U.S. Forces Korea toward strengthening containment of China (40.5% approve, 18% strongly approve). Conversely, opposition stood at 35.6% (opposed 29.6%, strongly opposed 6%), while only 5.9% of respondents took a neutral stance. These results indicate that a majority of South Koreans hold a positive view of expanding the role of USFK. This reflects a shift in perception, moving away from the traditional stance that USFK's role should be limited to defending the Korean Peninsula, and instead showing forward-looking support for this new role change aimed at containing China.

In this context, what patterns emerge in public perceptions regarding the role of the ROK-U.S. alliance? According to [Figure 2], 40.1% of respondents believed the alliance should be limited to its traditional role of responding to North Korea's military threats (Strongly agree: 10.3%, Somewhat agree: 29.8%). Conversely, 55.8% of respondents perceived that the alliance should play a more active and broader role, such as countering China's challenges in the Indo-Pacific region (Strongly agree 24.4%, Agree 31.4%). Only 4.1% expressed a neutral opinion.

The findings from [Figure 1] and [Figure 2] present significant implications for discussions on modernizing the ROK-U.S. alliance. They indicate a structural shift in public perception regarding the alliance's role. It is noteworthy that approximately 60% of South Koreans perceive that the role of USFK and the ROK-US alliance should extend beyond traditional defense of the Korean Peninsula (deterrence against North Korea) to encompass the entire Indo-Pacific region. This indicates that Koreans' perspective on the alliance is moving beyond a limited, Korean Peninsula-centric framework, demonstrating a willingness to embrace comprehensive security cooperation at the regional level.

[Figure 2]: South Koreans' Perception of the Role of the ROK-U.S. Alliance

3. Perceptions of the Changing Role of US Forces in Korea: Theoretical Discussion of Driving Factors

What factors then trigger shifts in the Korean public's perception regarding the enhanced role of US Forces in Korea in countering China? This report aims to analyze the influence of specific factors within three broad categories: (1) perceptions of US policy, (2) perceptions of security threats, and (3) perceptions of China policy.

3.1. Perceptions of U.S. Policy and Views on the Changing Role of U.S. Forces in Korea

The expansion of U.S. Forces Korea's role in countering China is a result of shifts in U.S. strategy toward China. In the unfolding U.S.-China strategic competition, driven by China's growing national power, the United States has designated China as its core competitor and is pursuing a strategy of denial to block China's expansion of influence in the region (Jeon Gyeong-ju 2025). This is based on the strategic objective of maintaining U.S. global leadership by preemptively preventing China from securing military superiority in the Indo-Pacific region. As China's economic growth fuels its military expansion, its anti-access/area denial (A2/AD) capabilities within the Indo-Pacific have significantly improved. As China's military power develops to a level posing a substantive challenge to the United States, Washington is substantially adjusting its regional troop deployments to prevent China from establishing military dominance within the First Island Chain. Within this strategic shift, the change in the role of US Forces Korea in countering China is directly linked to US defense of Taiwan and connects to the core US objective of deterring China within the First Island Chain (Jeon Jae-sung 2025).

Basic trust in the United States is predicted to be the most fundamental and crucial factor in shaping South Koreans' perceptions regarding the changing role of U.S. Forces Korea for containing China. According to an August 2025 public opinion poll, 66.5% of respondents perceived the United States as a trustworthy partner for South Korea, while 30.2% did not. This suggests that the higher the level of trust in the United States, the greater the likelihood of South Korean public support for changes in U.S. security strategy aimed at containing China. Furthermore, trust in the United States' extended deterrence capabilities for South Korea's defense could also be influenced. The traditional role of US Forces Korea (USFK) has been to serve as a tripwire deterrent against North Korean military provocations. If part of USFK were to be redeployed for China containment missions, concerns could arise about a weakening of deterrence against North Korea. Amid North Korea's advanced nuclear missile capabilities posing a grave threat to South Korean security, the US nuclear umbrella remains a fundamental pillar of South Korea's security policy for deterring North Korea. According to an August public opinion poll, 56.5% of respondents believed the U.S. nuclear umbrella could guarantee South Korea's security against North Korean threats, while 34.1% held a negative view. In this context, it can be anticipated that the higher the trust in U.S. extended deterrence, the greater the acceptance of shifting USFK's role toward containing China.

South Korean citizens' perceptions of U.S. foreign policy are shaped not only through security issues but also through economic factors. Amid intensifying U.S.-China strategic competition, the United States is focusing on rebuilding its economic foundations to enhance its competitiveness. Following the 2008 financial crisis and the 2020s pandemic, the U.S. economy continues to bear the dual burdens of fiscal deficits and trade deficits (Kim Hak-gyun 2025). Simultaneously, China's low-cost production structure and manufacturing competitiveness are accelerating the relative decline of U.S. manufacturing (Kim Su-eon 2025). Responding to these structural changes, the second Trump administration pursued the revitalization of the U.S. economy through tariff policies, and these protectionist measures were also applied to its ally, South Korea. Despite the Korea-U.S. Free Trade Agreement, the Trump administration announced it would impose high tariffs on South Korea. On August 1, 2025, it adjusted the mutual tariff rate from 25% to 15% conditional on South Korea's commitment to invest $350 billion in the U.S. According to opinion poll analysis, 81% of respondents assessed the U.S. high tariff policy on South Korean exports to the U.S. as inappropriate. South Koreans' negative perception of U.S. tariff policy is expected to lower support for the U.S. strategy to contain China through changes in the role of U.S. Forces Korea.

Furthermore, regarding South Korea's $350 billion investment in the U.S. to lower America's high tariffs, 55.6% of respondents viewed it negatively, while only 32.8% perceived it positively. This reflects South Korean citizens' resentment toward U.S. policies that impose economic burdens on allies for America's own economic benefit. Furthermore, the U.S. is restricting South Korea's science and technology-related trade and investment with China to secure an advantage in technological competition with China in advanced technology fields. The poll also found that 57.6% of respondents negatively evaluated U.S.-led export control policies targeting China. Overall, it is evident that the South Korean public negatively evaluates the United States' unilateral economic policies and the economic pressure exerted on its ally, South Korea. In this context, negative perceptions of the United States' large-scale investment pressure using tariffs as a weapon and South Korea's export control policies toward China to maintain U.S. hegemony are expected to heighten opposition to changes in the role of U.S. Forces Korea aimed at containing China.

3.2. Perceptions of Security Threats and Views on the Changing Role of US Forces in Korea

South Koreans' perception of security threats is also considered a key factor influencing public opinion on the role transition of US Forces Korea. In an August 2025 poll, South Korean citizens selected North Korea as the most militarily threatening nation, with 83.6% of respondents identifying North Korea as a threat to South Korea's security. South Korea remains the world's only divided nation, and with the Korean War still not formally ended, North Korea has continuously advanced its nuclear missile capabilities since Kim Jong-un took power. North Korea's adoption of a nuclear force policy law in September 2022 has heightened the possibility of its preemptive use of nuclear weapons. South Koreans' perception of North Korea as a security threat is expected to weaken support for changing the role of U.S. Forces Korea (USFK) to focus on countering China. As previously mentioned, USFK has primarily carried out the core mission of deterring North Korea. Therefore, shifting its role to counter China could significantly weaken the deterrence posture against North Korea.

Meanwhile, an August public opinion poll revealed that perceptions of China as a threat have spread significantly among the South Korean public, alongside concerns about North Korea's security threat. The poll found that 84% of respondents perceive China's military expansion as threatening. Particularly, military tensions between South Korea and China in the Yellow Sea have escalated recently as China unilaterally installed structures in the Yellow Sea's provisional numerical zone. It is reported that when the South Korean marine research vessel Onnuri approached the structures China installed in the West Sea, Chinese coast guard vessels systematically obstructed its access (Noh Seok-jo 2025). Furthermore, incursions by Chinese military aircraft into South Korea's Air Defense Identification Zone (KADIZ) are also on a continuous upward trend. China repeatedly justifies its unilateral incursions by arguing that the KADIZ is international airspace (Lee Seong-hoon 2024). Against this backdrop, the growing perception among South Koreans of China as a security threat is likely to translate into increased support for strengthening the US Forces Korea's role in countering China. This suggests an underlying recognition that US Forces Korea should be utilized more proactively to counter China's military expansion and security threats.

3.3. Public Perception of Public Policy and Views on the Changing Role of US Forces Korea

The final category concerns South Korean citizens' perceptions of China policy. As the Trump administration's second term intensifies U.S. tariff policies targeting South Korea and pressure on South Korean investment in the U.S., the importance of economic relations between South Korea and China is being highlighted once again. Traditionally, China has been a major export destination for South Korea, playing a crucial role in its economic growth. However, following the THAAD deployment incident, China's economic retaliation and internal economic restructuring driven by its rise have elevated China to a key competitor in South Korea's core industrial sectors. Consequently, economic cooperation between South Korea and China has indeed become somewhat strained compared to the past. Yet, as U.S. economic pressure intensifies, the importance of economic cooperation with China is resurfacing. According to an August public opinion poll, 53% of respondents felt the current level of economic cooperation between South Korea and China is appropriate, while approximately 33% believed economic cooperation should be strengthened. This emphasis on economic cooperation with China could potentially weaken support for enhancing the role of U.S. forces in South Korea as a deterrent against China. On the other hand, the public may perceive economic cooperation with China and China's security threats as separate dimensions. In other words, the public may hold the view that economic cooperation with China should proceed while China's military threats must be contained. From this perspective, it can be anticipated that the perception of strengthening economic cooperation with China will not significantly impact the perception of enhancing the USFK's role in containing China.

Another key factor shaping South Korean public perception of China policy is the possibility of a Chinese invasion of Taiwan. Concerns have been raised in various quarters about the potential for Xi Jinping to use force to unify Taiwan. Some analysts suggest that Xi may consider invading Taiwan to secure a strong justification for suppressing domestic political opposition, thereby ensuring his long-term rule. The general assessment is that the possibility of a Chinese invasion of Taiwan would have both direct and indirect impacts on the security environment of the Korean Peninsula. Should China engage in armed conflict with Taiwan, the United States is highly likely to intervene to defend Taiwan. Consequently, South Korea, as a U.S. ally, would also likely become involved in the Taiwan conflict. Furthermore, some viewpoints suggest that China might induce North Korea to engage in military provocations timed to coincide with a Taiwan invasion, through prior discussions with Pyongyang, to minimize South Korean and U.S. Forces Korea intervention in such a scenario. Amid the potential significant impact of a Chinese invasion of Taiwan on South Korea's foreign and security policy, polls indicate that a majority of South Koreans perceive a high likelihood of military conflict occurring in the Taiwan Strait in the near future. Nearly 72% of respondents predicted that China could engage in military provocations against Taiwan. Furthermore, 88% of respondents stated that military tensions and conflicts in the Taiwan Strait are important to South Korea's national interests. Considering this context—South Koreans' perception of the possibility of China's military unification of Taiwan and the importance of the Taiwan Strait to South Korea—it is anticipated that support for changing the role of USFK to counter China will increase.

4. Perceptions of the Changing Role of U.S. Forces in Korea: An Empirical Analysis of Driving Factors

To analyze the empirical influence of factors that could drive changes in the Korean public's perception of altering the role of USFK, this report employed quantitative analysis methods. The dependent variable was set as the level of support among South Korean citizens for changing the role of USFK to strengthen containment of China, as described earlier. The independent variables were set as factors belonging to the three categories described above: (1) perceptions of US policy, (2) perceptions of security threats, and (3) perceptions of public policy. Independent variables related to perceptions of U.S. foreign policy included: trust in the U.S. as Korea's partner; trust in the U.S. nuclear umbrella for Korea's defense; perceptions of U.S. tariff policies imposed on Korea; perceptions of U.S. pressure on Korea to increase investment in response to tariff rate cuts; and perceptions of U.S. export controls on Korea's exports to China. Independent variables related to security threat perceptions included the perceived security threat levels from North Korea and China. Finally, the independent variables related to perceptions of public diplomacy policy included perceptions of South Korea-China economic cooperation, the possibility of a Chinese invasion of Taiwan, and the perceived impact of a Taiwan Strait crisis on South Korea's national interests. This is summarized in the table below.

[Table 1]: Empirical Analysis Variable Specification