[EAI Issue Brief] Security Threats and the Strategic Rediscovery of Japan: Analysis of Public Perception on Strengthening Bilateral Cooperation between Korea and Japan Based on the 1st Korea-US-Japan Public Mutual Perception Survey

I. Introduction

On August 23, President Lee Jae-myung and Japanese Prime Minister Shigeru Ishiba held a summit and agreed on the importance of pursuing "unwavering cooperation between Korea and Japan, and among Korea, the US, and Japan." This meeting was evaluated as unusual because it was the first summit held in Japan since his inauguration, and the results were published in a document for the first time in 17 years. Furthermore, considering the policy stance towards Japan that President Lee Jae-myung and the ruling party showed before taking office, this move was seen as an unexpected shift. This can be interpreted as the South Korean government having a strong will to strengthen cooperation between Korea and Japan and, through this, to strengthen trilateral cooperation among Korea, the US, and Japan. If so, what is the South Korean public's stance on strengthening cooperation between Korea and Japan? Will they accept the government's move to strengthen cooperation?

Cooperation between Korea and Japan has been difficult to develop organically at the bilateral level due to historical issues and anti-Japanese sentiment for a long time, and has primarily proceeded within the framework of trilateral cooperation mediated by the United States. This is also a product of the 'hub and spokes' system that the US established in East Asia during the Cold War (Cha 2009). Within this structure, cooperation between Korea and Japan has always progressed through US mediation and persuasion, and Korea-Japan relations have been perceived as the weak link in Korea-US-Japan cooperation.

However, recent self-centered actions by the US and its reduced engagement in alliances make it difficult to manage regional security issues solely through the existing 'hub and spokes' model. These changes provide an important background for understanding President Lee Jae-myung's visit to Japan and the message of strengthening cooperation put forth by both Korea and Japan. So, how will the South Korean public accept this move to strengthen cooperation between Korea and Japan? In the past, there have been numerous instances where the public rejected attempts at improving relations at the government level, leading to boycotts of Japanese products, anti-Japanese protests, and even anti-government demonstrations. Therefore, in 2025, has a shift in public perception regarding the level of cooperation between Korea and Japan, as demonstrated by the Lee Jae-myung administration, actually occurred in public perception?

Public opinion does not directly determine foreign policy, but it is significant in that it limits the range of policy options available to decision-makers and influences the momentum of policy implementation.[1] From this perspective, this paper analyzes South Korean public perception of bilateral security and economic cooperation between Korea and Japan, utilizing data from the 1st Korea-US-Japan Public Mutual Perception Survey (N=1,585) conducted in August 2025. Specifically, it verifies through logistic regression analysis the correlation between the perception of threats from North Korea and China and support for cooperation between Korea and Japan, while also examining their effects by including Japan's favorability and trust in the US as control variables. Furthermore, by comparing the factors influencing public opinion on bilateral security cooperation between Korea and Japan and trilateral security cooperation among Korea, the US, and Japan, it investigates how public threat perception differentially affects these two cooperation frameworks.

II. Public Opinion Distribution on Bilateral Cooperation between Korea and Japan: Positive Opinion Dominates

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

Before proceeding with the regression analysis, we first examine the distribution of opinions on strengthening bilateral cooperation between Korea and Japan. According to the survey, opinions favoring the strengthening of bilateral cooperation between Korea and Japan were dominant. [Figure 1] shows the responses to the question, "Do you think security cooperation between Korea and Japan should be strengthened compared to the current level?" A total of 75.5% of 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.' Regarding negative responses, 12% answered 'generally negative,' and 2.9% answered 'very negative.' Meanwhile, 9.6% held a neutral stance.

As can be seen in [Figure 2], economic cooperation between Korea and Japan received even higher support than security cooperation. To the question, "Do you think economic exchange and cooperation between Korea and Japan should be strengthened compared to the current level?", 85.6% of all respondents evaluated it positively. Among them, 23.6% chose 'very positive,' and 62% chose 'generally positive.' On the other hand, 5.9% chose 'generally negative,' and 0.9% chose 'very negative,' resulting in only 6.8% holding a negative stance. Neutral opinions, such as 'neither,' accounted for 7.6%.

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

Comparing the two areas, economic cooperation received approximately 10% higher support than security cooperation, and negative and neutral responses were lower in the economic cooperation sector. In summary, it can be seen that the South Korean public is generally positive about strengthening bilateral cooperation with Japan in both security and economic fields compared to the current level. In particular, they appear to hold a more proactive attitude towards economic cooperation.

III. Patterns of Support for Cooperation between Korea and Japan Based on Threat Perception: Comparative Analysis of Security and Economic Cooperation

Do South Koreans perceive Japan as a strategic partner for jointly responding to security threats? This section examines, through regression analysis, whether the high support for bilateral cooperation between Korea and Japan is correlated with the perception of security threats. To this end, four perceptions related to South Korea's foreign and security environment were included as key explanatory variables.

First, the perception of threat from North Korea. In a situation where North Korea's nuclear capabilities are posing a direct threat to both Korea and Japan, we examine whether the perception of this threat leads to the need for strengthening cooperation with Japan. The joint press statement by the leaders of Korea and Japan highlighted cooperation on the Korean Peninsula's peace and North Korean issues as important agendas for bilateral cooperation. We examine whether the South Korean public accepts this direction of cooperation.

Second, to examine whether South Koreans perceive Japan as a partner for jointly responding to threats from China, the perception of threat from China was included. As 73% of South Koreans identified China as a military threat in this survey (Son Yeol, Oh In-hwan, and Lee A-rim 2025), the perception of threat from China is the second highest after North Korea. Accordingly, we examine whether the perception of threat from China leads to support for cooperation with Japan.

Third, trust in the United States was included as a control variable. Given that cooperation between Korea and Japan has primarily progressed under US leadership and mediation, the possibility that perceptions of the US influence attitudes toward cooperation with Japan was considered. Fourth, favorability towards Japan is also an important variable. Considering that sentiment towards Japan may influence the preference for policies such as cooperation between Korea and Japan, favorability towards Japan was controlled. In addition, respondents' gender, age, ideological orientation, income level, and education level were controlled.

1. Security Cooperation: The more threats are perceived from North Korea and China, the more positive the attitude towards security cooperation with Japan.

The analysis of attitudes toward bilateral security cooperation between Korea and Japan revealed that the more North Korea and China are perceived as threats, the more positive the attitude toward bilateral security cooperation with Japan becomes.[2][Figure 3] presents the marginal effects of the four key variables on support for bilateral security cooperation between Korea and Japan. First, perceiving North Korea as a threat increases the probability of supporting security cooperation between Korea and Japan by 16.4%. Second, respondents who perceive China as a threat are 5.2% more likely to support security cooperation between Korea and Japan than those who do not. These results go beyond existing research (Jeong Sang-mi 2023) which found that perceptions of threat from North Korea and China promote support for trilateral security cooperation among Korea, the US, and Japan in analyses of perception surveys from 2018-2021, and show that they can also positively influence support for bilateral security cooperation between Korea and Japan. This suggests that public threat perception can serve not only as a basis for supporting trilateral cooperation but also as a driving force for bilateral cooperation. This implies that the government's move to strengthen cooperation has a certain level of public support.

[Figure 3] Bilateral Security Cooperation between Korea and Japan: Marginal Effects of Key Variables

Third, trust in the United States positively influenced support for security cooperation between Korea and Japan. This suggests that the public may perceive cooperation with Japan as an extension of the Korea-US alliance or as complementary to trilateral cooperation among Korea, the US, and Japan. Fourth, favorability toward Japan showed the largest influence among the key variables. This indicates that emotional responses toward Japan are strongly projected onto policy preferences for security cooperation. According to the 2025 EAI survey, 52.4% of respondents had a favorable impression of Japan, surpassing unfavorable opinions for the first time and reaching an all-time high (Son Yeol, Oh In-hwan, and Lee A-rim 2025). If relations between the two countries remain stable and the positive image of Japan continues, public acceptance of bilateral security cooperation is likely to remain high.

2. Economic Cooperation: The threat from China has a greater effect on economic cooperation than on security cooperation.

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

[Figure 4] presents the influence of key variables on bilateral economic cooperation between Korea and Japan. The threat from North Korea showed a positive correlation with economic cooperation between Korea and Japan (10.4% increase in probability of agreement), but its influence was somewhat weaker than in security cooperation (16.4%). On the other hand, the influence of the threat from China was observed to be greater in economic cooperation than in security cooperation. When China is perceived as a threat, the probability of agreeing to bilateral economic cooperation between Korea and Japan increases by 7.2%. Trust in the United States also showed a positive correlation (3.4% increase in probability of agreement), but its influence decreased compared to its effect on security cooperation (8.1%). Favorability toward Japan still showed high explanatory power, but its influence in economic cooperation (16.9%) was also lower than in security cooperation (20.5%).

These differences in the influence of variables by type of cooperation suggest a difference in the logic of response according to the nature of the threat. The threat of North Korea's nuclear and missile programs is direct and has a strong military character, thus potentially stimulating a greater demand for security cooperation. In contrast, the perception of threat from China is less direct than the security threat from North Korea, and it is interpreted that its influence is relatively greater in the economic cooperation domain due to the complex interplay of economic pressure and military assertiveness. Given the reality of high economic interdependence with China, the South Korean public may have perceived economic cooperation with Japan as a measure to cope with economic uncertainties. Furthermore, the relatively reduced influence of Japan's favorability in economic cooperation indicates that sensitivity to sentiment towards Japan is lower in the economic domain, and pragmatic considerations play a stronger role.

3. Bilateral Security Cooperation between Korea and Japan vs. Trilateral Security Cooperation among Korea, US, and Japan: Marginal Effects of Key Variables

[Figure 5] compares the influence of each variable on bilateral security cooperation between Korea and Japan (red bars) and trilateral security cooperation among Korea, the US, and Japan (blue bars). The most notable finding is the difference in the influence of China threat perception. 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, a difference of 1.7 times. This appears to reflect the public's perception that the trilateral cooperation framework, including the US, is more effective in responding to the rise of China. On the other hand, the threat from North Korea showed the greatest influence in both bilateral (16.4 percentage points) and trilateral (16.3 percentage points) cooperation, appearing at almost the same level. These results show that the threat from North Korea serves as a common support base for both bilateral cooperation between Korea and Japan and trilateral cooperation among Korea, the US, and Japan. Furthermore, it can be predicted that public acceptance will be high if security cooperation between Korea and Japan is strengthened to counter the threat from North Korea.

Favorability toward Japan positively influenced both bilateral and trilateral cooperation, but the effect was more pronounced in bilateral security cooperation between Korea and Japan. This suggests that bilateral security cooperation may be more influenced by emotional factors toward the partner country. In contrast, the perception of threat from China has relatively greater explanatory power for trilateral security cooperation among Korea, the US, and Japan than for bilateral security cooperation between Korea and Japan. While bilateral cooperation is more sensitive to emotional factors, the relative importance of structural threat factors increases in trilateral cooperation.

IV. Conclusion

The analysis results presented above offer the following implications. First, the fact that perceptions of threat from North Korea and China lead to support not only for security cooperation among Korea, the US, and Japan but also for bilateral cooperation between Korea and Japan indicates that South Koreans view Japan as a strategic partner for jointly responding to security threats. To date, cooperation between Korea and Japan has primarily progressed within the framework of trilateral cooperation through US mediation and persuasion. However, if the positive perception of cooperation with Japan confirmed in this analysis continues, it suggests the possibility that bilateral cooperation between Korea and Japan could develop into a cooperative axis with its own momentum, moving beyond the subordinate framework of trilateral cooperation.

[Figure 5] Comparison between Bilateral Security Cooperation between Korea and Japan and Trilateral Security Cooperation among Korea, US, and Japan

Second, favorability toward Japan showed a very significant influence in both bilateral security cooperation and economic cooperation between Korea and Japan. This indicates that public perception of cooperation is heavily influenced not only by security calculations but also by emotional factors. Therefore, if Korea-Japan relations are managed stably and anti-Japanese sentiment does not re-ignite, public acceptance of strengthened cooperation will remain at a high level. Conversely, if historical issues or other conflict points re-emerge, a decline in favorability could directly lead to a weakening of support for cooperation, requiring caution.

Finally, it is worth observing whether the US's self-centered actions, if continued, will increase public antipathy and concern, thereby acting as a driving factor for the need for cooperation with Japan in the perceptions of South Koreans. This analysis currently shows that trust in the US and attitudes toward cooperation with Japan are closely linked. Through this, it was confirmed that trilateral cooperation among Korea, the US, and Japan is currently perceived as a complementary relationship. However, if the US's engagement with alliances further weakens or if the burden on allied nations increases due to unilateral policy implementation, the trend of perceiving bilateral cooperation with Japan not only within the framework of trilateral cooperation but also as a complementary axis may strengthen. Whether this change will materialize will likely depend on the direction of US foreign policy, the security environment surrounding the Korean Peninsula, and the relationship management capabilities of both Korea and Japan. ■

References

Son Yeol, Oh In-hwan, and Lee A-rim, eds. "Analysis of the Results of the 1st Korea-US-Japan Public Mutual Perception Survey and the 12th Korea-Japan Public Mutual Perception Survey in 2025." EAI Public Opinion Briefing. East Asia Institute, August 28, 2025.https://www.eai.or.kr/new/ko/pub/view.asp?intSeq=23414&board=kor_issuebriefing&keyword_option=&keyword=&more=

Jeong Sang-mi. "Security Threats and Perceptions of Japan: Analysis of Public Opinion on Improving Korea-Japan Relations and Trilateral Security Cooperation among Korea, US, and Japan (2018-2021)." Korea and World Politics 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 Security34, no. 3 (2010): 158-196.

[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.

■ Author: Jeong Sang-mi_Research Professor, Center for Geopolitical Studies, Korea National Diplomatic Academy.

■ Responsible Editor: Lee Sang-jun_EAI Researcher
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