政策研究大学院大学 / National Graduate Institute for Policy Studies博士（国際関係論） / Ph.D. in International Relations論文審査委員: 道下 徳成（主査）, 岩間 陽子, 竹中 治堅, CHOI Kyungwon（常葉大学）, 隅藏 康一application/PDF安全保障・国際問題プログラム / Security and International Studies Programdoctoral thesi

KIM, Ju-Hyung

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Insitutional Repository at the National Graduate Institute for Policy Studies

1   Japan’s Security Contribution to South Korea, 1950 to 2023   Kim Ju-hyung  National Graduate Institute for Policy Studies (GRIPS)    Introduction While it is evident that the defense of South Korea is assured by the US-ROK Mutual Security Treaty, the role of Japan in South Korea’s defense remains relatively unclear to general public. From the perspective of most South Koreans, Japan’s involvement during the Korean War, where Japan served as a crucial launching pad for UN forces to the Korean peninsula, and the establishment of the Pohang steel mill utilizing the “claims fund” provided by Japan after signing the 1965 Treaty on Basic Relations Between Japan and the Republic of Korea, are generally understood as contributions to South Korea’s national interest. Nevertheless, these events are often viewed as isolated occurrences, and the idea of Japan’s security contribution to South Korea is met with resistance by many Koreans due to the historical issues stemming from Japan’s 35-year colonial era, which still elicits strong emotions to this day. Furthermore, the absence of a formal military alliance between Japan and South Korea, along with Japan’s constitutional restrictions on maintaining a regular military, has limited the exploration of the comprehensive security cooperation between the two nations or Japan’s overall security contribution to South Korea.  Regarding Japan’s security contribution to South Korea, numerous questions arise, such as: (1) the nature of these contributions, whether they were one-time events or recurring; (2) the trend of these contributions over time, whether they increased or decreased; (3) the role of the United States in influencing Japan’s assistance to South Korea when the need arose; (4) the form in which these security contributions were made, whether they were direct or indirect; (5) the specific types of contributions made; (6) whether North Korea’s provocations towards South Korea served as triggers for Japan’s security contributions; (7) the key motivations behind Japan’s decisions to provide such support to South Korea. The primary goal of this study is to explore these questions by conducting hypothesis tests and identifying patterns concerning Japan’s security contribution to South Korea.  2  Hypothesis In my study, I examined the four hypotheses below to understand Japan’s rationale for offering security contribution to South Korea.  Hypothesis 1. Japan’s commitment to South Korea’s security hinges on its desire to gain the approval of the United States. Whenever Japan seeks to garner favor from the United States, it tends to elevate its security contributions to South Korea. Conversely, when Japan does not have the need to gain favor from the United States, it tends to reduce its security commitments to South Korea. Hypothesis 2. Japan’s security support for South Korea is based on its assessment of the North Korean threat to South Korea. When Japan perceives that the North Korean threat to South Korea is significant, it tends to amplify its security contributions to South Korea. Conversely, when Japan assesses that the North Korean threat to South Korea is minor, its inclinations to reduce its security contributions to South Korea becomes more apparent. Hypothesis 3. Japan’s security contribution to South Korea depends on Japan’s evaluation of the United States’ defense commitment to South Korea. When Japan perceives a less robust US defense commitment to South Korea, it is more likely to increase its security support for South Korea. Conversely, when Japan perceives a strong US defense commitment to South Korea, its inclination to bolster its security contributions to South Korea diminishes. Hypothesis 4. Japan’s security contribution to South Korea is influenced by the strength and vocal opposition of Socialist and Communist factions within Japan to the government’s security policies. When these factions hold significant sway and openly challenge Japan’s security policies, it tends to limit Japan’s security contributions to South Korea. Conversely, when the Socialist and Communist factions do not strongly oppose the Japanese government, Japan’s security contributions are less constrained.   Findings By conducting extensive research, including the collection of data from primary and secondary sources such as government documents, public statesments, memoirs, and other published materials from the United States, Japan, and South Korea, as well as conducting over 60 interviews with security experts, this study has identified six key findings regarding the reasoning why Japan contributed to the security of South Korea: (1) Japan extended security support to South Korea to win favor from the United States; (2) Japan intensified its security efforts for South Korea in response to a perceived significant North Korean threat; (3) The fear 3  of US abandonment is the third most important determinant influencing Japan’s contributions; (4) Japan consistently made security contributions throughout the analyzed timeframe, irrespective of the state of Japan-ROK relations; (5) The strength or vocal opposition of Socialist and Communist factions did influence Japan’s security contributions to South Korea.    Japan extended security contributions to South Korea strategically, particularly when seeking favor from the United States, even if it involved a tradeoff. This tradeoff entailed Japan selectively determining the nature of its contributions, without fully adhering to all of the US’ demands and/or expectations. Significant instances of Japan seeking favor from the United States were particularly pronounced in the early years of the Korean War. This objective was evident in Prime Minister Yoshida’s efforts to secure favorable terms for the San Francisco Treaty, a stance observed by high-ranking officials including Director Okubo Takeo. Despite Japan’s official policy of cooperation with the United Nations and offering full support to the United States, this cooperation was selective. For instance, Japanese political leaders strongly opposed the idea of allowing Japanese “volunteers” to participate in the Korean War. In July, Yoshida, stated that Japan had renounced the right to engage in belligerent action and emphasized Japan’s commitment to peace. In this context, Yoshida instructed that the minesweeping operation be conducted discreetly, with a low-profile approach, and without public knowledge. Another instance of Japan seeking favor from the United States can be observed in the late 1960s to early 1970s when Japan pursued the return of sovereignty over Okinawa. Prime Minister Sato recognized the importance of Okinawa’s reversion and made it a major political issue, emphasizing that the return of Okinawa to its homeland was crucial to concluding the post-war period for Japan. However, this approach raised concerns in both the United States and South Korea regarding potential limitations on the US forces’ use of Okinawa as a launching and logistic pad in the event of a Korean contingency. Eventually, in 1969, Prime Minister Sato acknowledged the significance of South Korea to Japan’s security and promised that Tokyo would respond “positively and promptly” to request from the United States to use bases in Japan, including Okinawa, in a Korean contingency. Despite critics in Japan (this group encompasses members of the Socialist Party, including figures like Saburo Eda, as well as residents of Okinawa) arguing that allowing Okinawa’s bases to be used in a Korean contingency was too high a price for the reversion, the US presence was maintained, and Okinawa continued to serve as a crucial launching pad for US forces in the Far East. Japan increased its security contributions to South Korea in response to a perceived significant North Korean threat. Whenever an incident or development originating from North Korea was deemed detrimental to South Korean security from the Japanese perspective, Japan 4  took measures to help the South Koreans. During the Korean War, Japan took the threat posed by North Korea to South Korea very seriously. For example, in July 1950, Prime Minister Yoshida expressed during a session of the Japanese Diet that South Korea was currently in chaos, with communist advancing toward Japan’s vicinity. Even after signing of the 1953 Armistice Agreement, Japan continued to view the possibility of an all-out war from North Korea against South Korea with great concern. The 1963 Mitsuya Study conducted by JSDF envisaged a full-scale attack by North Korea on South Korea, indicating Japan’s genuine belief in the conventional threat posed by North Korea. This perception persisted from 1969 to 1995, with incidents like the Pueblo abduction and the Blue House raid in 1968 leading Prime Minister Sato to underscore the serious threat to South Korean defense, which was closely related to Japan’s national interest. Despite intentions to cooperate with the South Korean government, Japan did not fulfill South Korea’s request for counter-guerrilla equipment in 1968, highlighting Japan’s adherence to its pacifist constitution and avoidance of direct contributions to South Korea's security. Following the partial resolution of the first North Korean nuclear crisis through the Agreed Framework in 1994, Japan’s perception of the North Korean threat somewhat diminished. However, in 2015-2023, Japan witnessed a rise in its perception of the North Korean threat to South Korea. While acknowledging North Korea’s conventional forces’ inferiority to those of the US Forces Korea and South Korea, Japan believes that North Korea’s pursuit of weapons of mass destruction and missiles presents a grave and immediate risk to South Korea’s security, as indicated in the Japanese defense white paper.    When the United States’ security commitment to South Korea decreased, there was a noticeable upswing in Japan’s security contributions to South Korean defense. Nevertheless, Japan’s security contribution did not necessarily wane even when the United States increased its security commitment to South Korea. Concerning Japan’s perception of the weakened commitment of the United States to South Korean defense, two significant instances stand out—the declaration of the Nixon Doctrine in 1969 and the inauguration of the US presidency by Carter in 1977. During these events, Japan perceived a diminishing commitment from the United States to South Korean defense. Before the withdrawal of the US Seventh Infantry Division from South Korea in March 1971, based on the Nixon Doctrine, the Japanese government expressed concerns. For example, in July 1970, Prime Minister Sato conveyed to Secretary of State William Rogers that the reduction of US military presence would have a substantial impact, emphasizing the delicate timing of such a decision. Additionally, on July 13, 1970, Nakasone, the head of the Defense Agency, voiced negative sentiments about the 5  reduction of US military presence in South Korea in the Japanese Diet. Similarly, on July 30, 1970, the Japanese Foreign Ministry requested the United States to reconsider the reduction of USFK. Japanese Ambassador to the United States Shimoda Takeso emphasized that the reduction should not be solely judged by numerical figures and that it could undermine South Korea’s psychological confidence. Nevertheless, Japan ultimately accepted the US troop reduction and considered providing economic assistance to South Korea. However, Japan opted not to furnish military hardware, particularly anti-guerrilla weapons, to South Korea. Similar patterns were observed when Carter became US president in 1977. In March 1977, Prime Minister Takeo Fukuda expressed opposition to the withdrawal of USFK, citing concerns about stability on the Korean peninsula during a discussion with President Carter. However, during Fukuda’s meeting with Vice President Walter Mondale that year, Fukuda changed his stance from staunch opposition to a neutral stance, treating the USFK withdrawal as a matter between the United States and South Korea. Fukuda also showed reluctance in offering direct military assistance, such as military hardware, to South Korea. This suggests that while Japan harbored concerns about the US commitment to South Korea in both situations, it favored adhering to the principles of the Yoshida Doctrine and remained hesitant to directly engage in bolstering South Korea’s defense sector, for example, by providing military equipment. Hypothesis 3 aligns well with the late 1960s and 1970s, as during that period, Japan was more inclined to increase its security support for South Korea when it perceived a weaker US defense commitment. However, this alignment is not as strong in the 1980s and 2010s, as Japan’s inclination to bolster its security contributions to South Korea did not decrease even when it perceived a strong US defense commitment. In fact, it was during the Reagan administration in the 1980s, a period when the United States’ defense commitment was indisputably at its strongest in modern history, that Japan chose to engage in economic cooperation for security purposes and pledged $4 billion loan to South Korea. Additionally, Japan’s significant enhancement of its potential in the operational and logistical fields took place during the Obama administration in the 2010s, a time when US defense commitment was remained stable; although it may have been as strong as during the Reagan administration, it was nowhere near the level during the Nixon, Ford, and Carter administrations. Findings in this study contradicts Victor Cha’s theory, which posits that Japan and South Korea would align less when the United States had a robust defense commitment in the Far East. Victor Cha’s claim, proposing that Japan heightened its security contribution to South Korea in response to reduced US security commitment, and conversely, diminished its contributions when the US commitment increased, is consistent with patterns observed in the late 1960s and 1970s. During this era, Japan exhibited a stronger willingness to enhance its security support 6  for South Korea when it perceived a diminished commitment from the United States. However, this correlation is less conspicuous in the 1980s and 2010s, as Japan’s propensity to bolster its security contributions to South Korea did not wane, or even increased, even in the presence of a robust US defense commitment during the Reagan and Obama Administrations.   Japan’s commitment to South Korea’s security was not significantly influenced by ups and downs in Japan-South Korea relations although there are some indications that Japan’s commitment tends to increase when the relations between Japan and South Korea are positive. It is crucial to highlight, however, that Japan’s dedication to security remained largely unchanged, even during periods of strained or unfavorable relations between the two countries.   Meanwhile, the influence and vocal opposition of Socialist and Communist factions did impact Japan’s security contributions to South Korea, both during the Cold War and the post-Cold War era. This influence was exerted through “invisible constraints” established by Japanese Socialist and Communist factions, factors that defense decision-makers in Japan had to consistently weigh throughout the post-war period. For instance, numerous security-related agreements and documents had to be kept confidential during the Cold War era due to prevailing public sentiments influenced by anti-war and pacifist ideologies associated with Socialist and Communist factions. Certain security documents, including the 1960 Secret Agreement, were not disclosed to the public. When their existence was leaked, as seen in the Mitsuya Study, the Prime Minister had to assure the public that it was not a government-sanctioned project and would not be integrated into the official defense plan. While having such contingency plans is not unusual for a sovereign nation, the necessity for secrecy was driven by the prevailing anti-war sentiments. These tendencies persisted into the post-Cold War era, even as Socialist and Communist factions diminished in influence. Although security agreements and documents were crafted and released to the public during this period, such as the Defense Guidelines and the 2015 Security Legislation, Japan’s defense policy-making procedures remained constrained by the legacy of the environment shaped by Socialist and Communist factions. For example, the need to revise the 1978 Defense Guidelines was acknowledged by both the United States and Japan, particularly after the 1993-94 North Korean nuclear crisis. However, the revision had to be postponed until 1997 due to public uproar, partly fueled by Socialist and Communist factions, triggered by the Okinawa rape incident in 1995. This delay was attributed to the lack of an appropriate political environment for Japanese policymakers to proceed with the Defense Guidelines revisions.  

Japan’s Security Contribution to South Korea, 1950 to 2023

https://grips.repo.nii.ac.jp/record/2000091/files/k288_summary_doc19111.pdf

Japan’s Security Contribution to South Korea, 1950 to 2023

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