I. Introduction

President Lee Jae-myung and Japanese Prime Minister Shigeru Ishiba held a summit meeting on August 23 and agreed on the importance of “promoting unwavering cooperation between South Korea and Japan, and among South Korea, the United States, and Japan.” This was unusual: it was the first post-inauguration summit held in Japan rather than the United States, and the first in 17 years to issue a written statement. Furthermore, considering the policy stance toward Japan shown by President Lee Jae-myung and the ruling party before taking office, this move was seen as an unexpected shift. This can be interpreted as the South Korean government’s determination to strengthen Korea–Japan cooperation and, through this, enhance trilateral cooperation among South Korea, the United States, and Japan. So, what stance do South Korean citizens hold regarding the strengthening of South Korea-Japan cooperation? Will they accept the government's moves to enhance this cooperation?

Korea-Japan cooperation has long struggled to develop organically at the bilateral level due to historical issues and anti-Japanese sentiment, proceeding primarily within the framework of trilateral cooperation mediated by the United States. This is also a product of the ‘hub and spokes’ system the United States established in East Asia during the Cold War era (Cha 2009). Within this structure, Korea-Japan cooperation has always advanced through U.S. mediation and persuasion, and Korea-Japan relations have been perceived as the weak link in trilateral cooperation.

However, recent U.S. moves toward self-centered policies and reduced engagement with allies have made it difficult to manage regional security issues solely through the existing ‘hub-and-spoke’ model. This shift provides crucial context for understanding President Lee Jae-myung's visit to Japan and the message of strengthened cooperation jointly put forward by South Korea and Japan. So, how will the Korean public perceive this movement toward enhanced Korea-Japan cooperation? In the past, when governments attempted to improve relations, the public often rejected such efforts, leading to numerous instances of boycotts of Japanese products, anti-Japan protests, and even anti-government demonstrations. Therefore, in 2025, is a shift in public perception regarding the level of Korea-Japan cooperation demonstrated by the Lee Jae-myung administration actually occurring?

Public opinion does not directly determine foreign policy, but it holds significant importance in that it limits the range of policies available to policymakers and influences the momentum for policy implementation.[1] With this context in mind, this paper analyzes Koreans' perceptions of bilateral security cooperation and economic cooperation between Korea and Japan using data from the first Korea-U.S.-Japan Public Perception Survey conducted in August 2025 (N=1,585). Specifically, it uses logistic regression analysis to examine the relationship between perceptions of threats from North Korea and China and support for Korea-Japan cooperation. It also includes favorability toward Japan and trust in the United States as control variables to assess their combined effects. Furthermore, by comparing the influencing factors on public opinion regarding bilateral Korea-Japan security cooperation and trilateral Korea-U.S.-Japan security cooperation, it clarifies how public threat perceptions differentially affect these two cooperative frameworks.

II. Public Opinion on Korea–Japan Bilateral Cooperation: Strongly Favorable

[Figure 1] Position on Strengthening Bilateral Security Cooperation between Korea and Japan 

Before conducting the regression analysis, we first examine the distribution of opinions regarding strengthening bilateral cooperation between South Korea and Japan. According to this survey, the prevailing view is that bilateral cooperation between South Korea and Japan should be strengthened beyond its current level. [Figure 1] shows responses to the question, “Do you think security cooperation between South Korea and Japan should be strengthened beyond the current level?” A total of 75.5% of all respondents expressed a positive stance, while negative responses accounted for only 14.9%. Specifically, 21.1% answered ‘very positive’ and 54.4% answered ‘generally positive’. Among negative responses, 12% answered ‘mostly negative’ and 2.9% ‘very negative’. Meanwhile, 9.6% expressed a neutral stance.

As shown in [Figure 2], economic cooperation between South Korea and Japan received higher support than security cooperation. When asked, “Do you think economic exchange and cooperation between South Korea and Japan should be strengthened beyond the current level?”, 85.6% of all respondents answered positively. Among these, 23.6% chose ‘very positive’ and 62% chose ‘generally positive’. Meanwhile, only 5.9% chose ‘mostly negative’ and 0.9% chose ‘very negative,’ meaning respondents with negative views accounted for just 6.8%. The neutral view of ‘neither’ accounted for 7.6%.

[Figure 2] Position on Strengthening Bilateral Economic Cooperation between Korea and Japan

Comparing the two areas, economic cooperation recorded approximately 10% higher support than security cooperation, with both negative and neutral responses being lower in the economic cooperation sector. Overall, it can be seen that the Korean public is generally positive about strengthening bilateral cooperation with Japan in the security and economic fields beyond the current level. Particularly, a relatively more proactive attitude was observed regarding the economic sector.

First, it concerns the perception of threat from North Korea. Given that North Korea's nuclear capability enhancement poses a direct threat to both South Korea and Japan, we examine whether this threat perception leads to a perceived need for strengthened cooperation with Japan. Joint statements by South Korean and Japanese leaders have highlighted cooperation on Korean Peninsula peace and North Korea issues as key agenda items for bilateral cooperation. We assess whether the South Korean public accepts this direction for cooperation.

Second, we included perceptions of China as a threat to examine whether Koreans view Japan as a partner for joint responses to threats originating from China. As 73% of Koreans identified China as a military threat in this survey (Sohn, Oh & Lee 2025), perceptions of China as a threat rank second only to those of North Korea. Accordingly, we examine whether perceptions of the China threat translate into support for cooperation with Japan.

Third, trust in the United States was included as a control variable. Given that Korea-Japan cooperation has primarily developed under U.S. leadership and mediation, we considered the possibility that perceptions of the United States could influence attitudes toward cooperation with Japan. Fourth, favorability toward Japan is also a crucial variable. Considering that sentiments toward Japan could influence preferences for the policy of Korea-Japan cooperation, favorability toward Japan was controlled. Additionally, respondents' gender, age, ideological orientation, income level, and education level were controlled.

1. Security Cooperation: Public Support Driven by Threats from North Korea and China

Analysis of attitudes toward bilateral security cooperation between South Korea and Japan revealed that the more respondents perceived North Korea and China as threats, the more positively they viewed bilateral security cooperation with Japan.[2] [Figure 3] presents the marginal effects of four key variables on support for bilateral South Korea-Japan security cooperation. First, perceiving North Korea as a threat increases the probability of supporting South Korea-Japan security cooperation by 16.4%. Second, respondents who perceive China as a threat are 5.2% more likely to support South Korea-Japan security cooperation than those who do not. These results extend beyond existing research (Jeong 2023) analyzing perception surveys from 2018 to 2021, which found that perceptions of North Korean and Chinese threats promote support for trilateral South Korea-U.S.-Japan security cooperation. They show that such threat perceptions can also positively influence support for bilateral South Korea-Japan security cooperation. In other words, public threat perceptions not only form the foundation for supporting trilateral cooperation but can also serve as a driving force for bilateral cooperation. This suggests that government efforts to strengthen cooperation have secured a certain level of public support.

[Figure 3] Japan-South Korea Bilateral Security Cooperation: Marginal Effects of Key Variables

Third, trust in the United States was found to positively influence support for South Korea-Japan security cooperation. This suggests the public may perceive cooperation with Japan as an extension of the ROK-U.S. alliance or as mutually complementary within the context of trilateral ROK-U.S.-Japan cooperation. Fourth, favorability toward Japan showed the strongest influence among key variables. This indicates that emotional responses toward Japan are strongly projected onto policy preferences regarding security cooperation. According to the 2025 EAI survey, respondents with a favorable impression of Japan reached 52.4%, surpassing unfavorable opinions for the first time and setting a record high (Sohn, Oh & Lee 2025). If bilateral relations remain stable and positive perceptions of Japan persist, public acceptance of bilateral security cooperation is likely to remain high.

2. Economic Cooperation: China Threat Exerts Greater Influence than in Security Cooperation

[Figure 4] Korea-Japan Bilateral Economic Cooperation: Marginal Effects of Key Variables

[Figure 4] presents the influence of key variables on bilateral economic cooperation between South Korea and Japan. The North Korean threat showed a positive correlation with South Korea-Japan economic cooperation (10.4% increase in probability of support), but its influence was somewhat weaker compared to security cooperation (16.4%). Conversely, the influence of the Chinese threat was observed to be greater in economic cooperation than in security cooperation. When China is perceived as a threat, the probability of supporting bilateral economic cooperation between South Korea and Japan increases by 7.2%. Trust in the United States also showed a positive correlation (3.4% increase in probability of support), but its influence was reduced compared to its effect on security cooperation (8.1%). Favorable views toward Japan still exhibited high explanatory power, but its influence on economic cooperation (16.9%) was also reduced compared to its effect on security cooperation (20.5%).

The differing influence of variables across these cooperation types suggests variations in response logic based on the nature of the threat. North Korea's nuclear and missile threats, being direct and strongly military in character, can stimulate a greater demand for security cooperation. Conversely, perceptions of threats from China are less direct than security threats originating from North Korea. Given the combined effects of economic pressure and military rise, this can be interpreted as exerting relatively greater influence in the realm of economic cooperation. Given the high level of economic interdependence with China, the South Korean public may have perceived economic cooperation with Japan as a countermeasure against economic uncertainty. Furthermore, the relatively diminished influence of Japan's favorability in economic cooperation indicates that sensitivity to anti-Japanese sentiment is lower in the economic sphere, where pragmatic considerations hold greater sway.

3. Bilateral vs. Trilateral Security Cooperation: China Threat Matters More for Trilateral Support

[Figure 5] compares the influence of each variable on bilateral South Korea-Japan security cooperation (red bars) and trilateral South Korea-U.S.-Japan security cooperation (blue bars). The most notable finding is the difference in the influence of the perception of China as a threat. When China is perceived as a threat, the probability of supporting bilateral security cooperation increases by 5.2 percentage points, while the probability of supporting trilateral security cooperation increases by 8.6 percentage points, showing a difference of 1.7 times. This appears to reflect the public's perception that a trilateral cooperation framework, including the United States, is more effective in responding to China's rise. Conversely, the North Korean threat exerted the greatest influence on both bilateral cooperation (16.4 percentage points) and trilateral cooperation (16.3 percentage points), with nearly identical levels of impact. These results demonstrate that threats originating from North Korea function as a common basis for support for both South Korea-Japan and South Korea-U.S.-Japan cooperation. Furthermore, it can be anticipated that strengthening South Korea-Japan security cooperation aimed at countering the North Korean threat would likely meet with high public acceptance.

Favorable views toward Japan positively influenced both bilateral and trilateral cooperation, though the effect was more pronounced in bilateral security cooperation between South Korea and Japan. This suggests that bilateral security cooperation may be more heavily influenced by emotional factors toward the partner country. Conversely, perceptions of threat from China exert relatively greater explanatory power in trilateral security cooperation among South Korea, the United States, and Japan than in bilateral security cooperation between South Korea and Japan. This demonstrates that while bilateral cooperation is more sensitive to emotional factors, the relative importance of structural threat factors increases in trilateral cooperation.

[Figure 5] Comparison between Bilateral Security Cooperation between South Korea and Japan and Trilateral Security Cooperation among South Korea, the United States, and Japan

IV. Concluding Remarks

The above analysis suggests the following implications. First, the fact that perceptions of threats from North Korea and China translate into support not only for trilateral security cooperation among South Korea, the U.S., and Japan, but also for bilateral cooperation between South Korea and Japan, indicates that South Koreans view Japan as a strategic partner for jointly responding to security threats. Until now, Korea-Japan cooperation has primarily advanced within the framework of trilateral cooperation, facilitated by U.S. mediation and persuasion. However, if the positive perception of cooperation with Japan identified in this analysis persists, Korea–Japan bilateral cooperation may develop into a distinct pillar with its own momentum, rather than remaining a subordinate framework within trilateral cooperation.

Second, favorable views toward Japan exerted a significant influence on both bilateral security cooperation and economic cooperation between South Korea and Japan. This demonstrates that public perceptions of cooperation are heavily influenced not only by security calculations but also by emotional factors. Therefore, if South Korea-Japan relations are managed stably and anti-Japanese sentiment does not reignite, public acceptance of enhanced cooperation will remain at a high level. Conversely, a resurgence of historical or other contentious issues could quickly erode favorability and, in turn, weaken support for cooperation—an outcome that warrants caution.

Finally, it remains to be seen whether continued U.S. self-centered actions will fuel growing public resentment and concern, potentially driving Koreans to recognize the necessity of cooperation with Japan. This analysis indicates that current trust in the U.S. and attitudes toward cooperation with Japan are closely interlinked. This indicates that, at present, trilateral cooperation among South Korea, the U.S., and Japan is perceived as mutually complementary. However, if the United States further reduces its alliance engagement or places greater burdens on allies through unilateral policies, perceptions may shift. Bilateral cooperation with Japan could come to be seen not merely within the trilateral framework, but also as a complementary axis in its own right. Whether such a shift materializes will likely depend on the direction of U.S. foreign policy, the security environment surrounding the Korean Peninsula, and the relationship management capabilities of both South Korea and Japan. ■

[1] Richard Sobel, The Impact of Public Opinion on U.S. Foreign Policy Since Vietnam. Oxford: Oxford University Press, 2001.

[2] All results mentioned in this paper are statistically significant at the 95% and 99% confidence levels.

References

Sohn, Yul, Inhwan Oh, and Ahlim Lee. "2025 EAI-API-KEI The 1st Korea-Japan-U.S. Joint Public Opinion Poll & the 12th Korea-Japan Joint Public Opinion Poll Result Analysis." EAI Public Opinion Briefing. August 28, 2025. https://www.eai.or.kr/new/ko/pub/view.asp?intSeq=23414&board=kor_issuebriefing&keyword_option=&keyword=&more=

Jeong, Sangmi. "Security Threats and South Koreans' Perception of Japan: Assessing Public Opinion on ROK-Japan Relations and the ROK-U.S.-Japan Security Cooperation." The Korean Journal of International Studies 63, no. 1 (2023): 177-219. https://doi.org/10.14731/kjir.2023.03.63.1.177

Cha, Victor D. "Powerplay: Origins of the US Alliance System in Asia." International Security 34, no. 3 (2010): 158-196.

■ Sangmi Jeong is a Research Professor at the Center for Geo-political Studies, Korea National Diplomatic Academy.

■ Translated and Edited by Sangjun Lee, EAI Research Associate

For inquiries: 02-2277-1683 (ext. 211) leesj@eai.or.kr