Deterioration of Sino–Japanese Relations and Future Prospects: Focusing on the Taiwan Issue

Kitae LEE

ktleekorea@sejong.org

Senior Research Fellow

Sejong Institute​

1. Background and Key Issues in the Deterioration of China-Japan Relations

One of the most notable developments in the recent international political environment of East Asia is the gradual deterioration of relations between China and Japan. Traditionally, China–Japan relations have been understood as a complex relationship characterized by the coexistence of both cooperation and conflict. The two countries have long faced multiple sources of tension, including historical disputes, territorial disagreements, and military competition. At the same time, however, they have maintained a certain degree of stability in their bilateral relationship through expanding economic cooperation and exchanges. In recent years, this balance has begun to weaken, with sources of conflict becoming increasingly pronounced. As a result, China–Japan relations appear to be gradually shifting toward a more structural form of strategic competition.

In particular, as strategic tensions surrounding the Taiwan issue continue to intensify, China–Japan relations are emerging as a key variable shaping the broader security order in East Asia, extending beyond a simple diplomatic dispute between the two countries. For China, the Taiwan issue represents a core matter of national sovereignty and territorial integrity. For Japan, it is increasingly viewed as a strategic issue directly linked to the regional security environment and the stability of vital sea lanes. For this reason, rising military tensions in the Taiwan Strait are no longer confined to the relationship between China and Taiwan alone, but are increasingly exerting direct influence on the security policies of surrounding states.

A major trigger that recently brought China–Japan tensions to the forefront was remarks on Taiwan made by Japanese Prime Minister Sanae Takaichi in November 2025. Prime Minister Takaichi publicly stated that a military conflict in Taiwan could constitute a security crisis directly linked to Japan's survival as a state. Such remarks indicate that Japan increasingly views the Taiwan issue not merely as a regional dispute but as a strategic matter closely connected to its own national security. This shift is widely interpreted as an important turning point in Japan's foreign policy, suggesting that Japan is moving beyond its traditionally cautious stance and beginning to articulate a more proactive security perspective regarding developments in the Taiwan Strait.

China responded strongly to these remarks. The Chinese government criticized Japan’s statements as interference in China’s internal affairs and lodged a formal diplomatic protest while signaling a range of potential countermeasures. The Chinese Ministry of Foreign Affairs summoned the Japanese ambassador to convey a strong protest, and Chinese state media also issued sharp criticism of Japan’s position. At the same time, Beijing raised the level of pressure on Tokyo by hinting at the possibility of expanded military activities and potential economic measures.

Recent tensions between China and Japan should therefore not be understood as the result of a single incident or political statement. Rather, they reflect the combined effects of several structural factors, including the intensifying strategic rivalry between the United States and China, rising tensions in the Taiwan Strait, and ongoing territorial disputes in the East China Sea. In this sense, the deterioration of China–Japan relations is better understood not as a temporary diplomatic dispute but as a manifestation of deeper structural tensions emerging from broader transformations in the East Asian regional order.

2. The 1952 San Francisco System vs. the 1972 China–Japan Normalization Order

To understand the nature of current China–Japan relations, it is necessary to examine the international order in East Asia that emerged after the Second World War. Following the war, Japan reentered the international community through the San Francisco Peace Treaty and simultaneously established a security alliance with the United States. In this process, Japan did not develop into an independent military power. Instead, it formed a security structure largely dependent on U.S. military capabilities and the American nuclear umbrella.

The U.S.–Japan alliance became the central foundation of Japan's security policy. While maintaining limited military capabilities, Japan relied on close cooperation with the United States to ensure its national security. This arrangement functioned as a key pillar of the East Asian security order during the Cold War. Through this alliance, the United States was able to maintain military bases in Japan and preserve its strategic presence in East Asia. At the same time, Japan was able to concentrate on economic development under the security guarantees provided by the United States.

Within this environment, Japan became one of the fastest–growing economies in the postwar world and emerged as a major economic power. Japan’s industrial technology and economic capabilities achieved strong competitiveness in global markets, and Japanese firms came to play an increasingly significant role in the international economy.

Meanwhile, relations between Japan and China reached a new turning point with the normalization of diplomatic relations in 1972. At the time, international politics was undergoing a significant shift marked by the improvement of U.S.–China relations, and Japan also moved to normalize its relations with China within this broader geopolitical context. Japan recognized the People's Republic of China as the sole legitimate government of China and severed its diplomatic relations with Taiwan.

Following this decision, Japan and China developed their relationship primarily through expanding economic cooperation. Japanese firms actively entered the Chinese market, and Japan's technology and capital played an important role in China's industrial development. At the same time, China provided Japanese companies with a vast market and a major production base.

However, this cooperative structure contained inherent contradictions. While Japan maintained its security alliance with the United States and remained positioned to balance China strategically, it simultaneously developed deep economic interdependence with China. This arrangement remained relatively stable for a period of time, but tensions gradually began to rise as China's economic and military power expanded rapidly.

3. Taiwan Contingency and Statements on a "Situation Threatening Survival"

One of the most notable recent changes in Japan's security policy is the significant shift in its perception of the Taiwan issue. Japan has increasingly begun to view the Taiwan issue as directly connected to its own national security. This shift can be understood as the result of several factors, including changes in the regional security environment in East Asia, the rapid growth of China's military capabilities, and the expanding strategic role of the U.S.–Japan alliance.

First, from a geographical perspective, the distance between Taiwan and Japan's southwestern islands is extremely short. As a result, if a military conflict were to occur in the Taiwan Strait, Japanese territory and surrounding waters would likely be directly affected. In particular, Okinawa could become a central theater of military tension, as the region hosts a large concentration of U.S. military bases.

The security of sea lines of communication (SLOC) also represents a critical factor. Japan imports the majority of its energy resources and raw materials from overseas, most of which are transported through maritime routes. The Taiwan Strait constitutes one of the key passages along these SLOCs. Consequently, a military conflict or maritime blockade in this area could have serious consequences for the Japanese economy.

In addition, the structure of the U.S.–Japan alliance plays an important role. If the United States were to intervene in the defense of Taiwan, Japan would likely participate in the operation in various ways, including providing military bases, logistical support, and intelligence sharing. Under such circumstances, Japan can no longer view the Taiwan issue merely as a regional conflict external to its own security concerns.

Finally, the rapid expansion of China's military capabilities has also played an important role in shaping Japan's changing security perceptions. China has significantly strengthened its naval and missile capabilities, thereby expanding its military influence in surrounding maritime areas. Notably, China's Anti–Access/Area Denial (A2AD) strategy is widely regarded as a capability that could restrict the military operations of the United States and Japan in the region. Under these circumstances, Japan has begun to move beyond its traditional defense–oriented strategy and has started to explore a more proactive deterrence posture.

A direct trigger for the recent deterioration of China–Japan relations has been Prime Minister Sanae Takaichi's effort to explicitly link the Taiwan issue to Japan's own national security. In particular, her public statement that "a Taiwan contingency could become a situation threatening Japan's survival" represents an important turning point in Japan's security policy. This remark was not merely diplomatic rhetoric. Rather, it carries significant implications because it politically clarified the possibility that Japan could become involved in a military crisis in the Taiwan Strait. In this sense, the statement suggests that Japan is moving beyond its traditionally cautious posture and is beginning to frame the Taiwan issue as one directly connected to its national survival.

The core significance of this statement lies in the political justification it provides for a more expansive interpretation of the conditions under which Japan could exercise the right of collective self–defense. Japan's constitution and security legislation have traditionally limited military action to defensive purposes. However, under the concept of a "situation threatening Japan's survival," military action may be justified even if Japan itself is not directly attacked, provided that circumstances threaten the country's survival. Therefore, if a military conflict in the Taiwan Strait were to affect Japan's sea lines of communication (SLOC), energy imports, or the operational capabilities of U.S. forces in the region, Japan could interpret such developments as a threat to its national security and claim a legal and strategic basis for military involvement.

Japan's sensitivity to the Taiwan issue is closely related to geographical and strategic factors. Taiwan is located very close to Japan's southwestern islands, and Japan's critical sea lines of communication (SLOCs) pass through the Taiwan Strait. Considering that the majority of Japan's energy imports depend on these maritime routes, a military conflict or blockade in the Taiwan Strait could deal a direct blow to Japan's economy and national security. Moreover, a military conflict in Taiwan would likely affect the operational capabilities of U.S. forces in the region, which in turn could weaken the deterrence capability of the U.S.–Japan alliance. For these reasons, Japan increasingly views the Taiwan issue not simply as a regional dispute but as a strategic matter directly connected to its national security.

Japan's recent statements should not be interpreted as referring only to the scenario of a full–scale Chinese invasion of Taiwan. The concept of a "situation threatening Japan's survival" encompasses a wide range of contingencies, including maritime blockades and gray–zone strategies, in addition to large–scale military conflict. Even if China does not launch a direct invasion of Taiwan, Japan could still regard disruptions to its SLOCs or intensified military pressure as a serious security threat. This interpretation suggests that Japan's security strategy is gradually shifting from a traditionally defense–oriented posture toward a more proactive deterrence strategy. Ultimately, Japan's statements regarding Taiwan should be understood not merely as diplomatic rhetoric but as a signal that Japan's broader security strategy and military policy are undergoing structural change.

These developments are part of broader efforts within the U.S.–Japan alliance to treat the Taiwan issue as a matter of joint strategic concern while also aiming to strengthen deterrence against China. At the same time, however, such moves have provoked strong reactions from Beijing and have contributed to the further deterioration of China–Japan relations.

4. China’s Assertiveness and Japan’s Response

Following Japan's statements regarding Taiwan, China has intensified pressure on Japan across multiple domains, including diplomacy, military activities, economic measures, and public discourse. China's response goes beyond the level of routine diplomatic protest and has increasingly contributed to transforming China–Japan relations into a form of structural strategic competition. In particular, China has expanded military activities targeting Japan while strengthening its military presence in both the East China Sea and the Taiwan Strait. The frequency of Chinese aircraft and naval vessels operating near Japan's Air Defense Identification Zone (ADIZ) has significantly increased. These activities function as a form of sustained strategic pressure that steadily raises the operational burden on Japan's Self–Defense Forces.

Such military pressure goes beyond routine training and increasingly resembles efforts to test operational capabilities under simulated real–world contingencies. China has continued to expand military activities in the East China Sea and around the Senkaku Islands, effectively probing Japan's defense posture while simultaneously attempting to establish new facts on the ground, or more precisely, at sea. This strategy appears designed not to provoke immediate military conflict but to gradually erode Japan's response capacity and reshape the regional strategic environment in China's favor over the long term.

China's pressure is not limited to military measures. Beijing has also employed economic instruments as part of its broader strategy toward Japan. Measures such as stricter quarantine inspections on certain Japanese products, import restrictions, and the reduction of tourism and educational exchanges have generated indirect economic pressure on Japan. Of particular concern is China's ability to regulate the supply of strategic resources, including rare earth elements, which is widely viewed as a tool that could have long–term implications for the stability of Japan's advanced industrial supply chains. These economic measures demonstrate how China increasingly combines political disputes with economic statecraft in managing its relations with Japan.

China has also actively employed historical issues and memory politics as part of its broader strategy. By re–emphasizing Japan’s militarist past and the issue of wartime responsibility, Beijing seeks to frame Japan’s evolving security policy in a negative light within the international community. China has highlighted controversies surrounding Japanese leaders’ historical perceptions, visits to the Yasukuni Shrine, and textbook disputes, conveying the message that Japan’s growing military capabilities could signal a revival of past militarism. This historical framing has become an important component of China’s external propaganda and diplomatic messaging.

In response, Japan has simultaneously pursued military strengthening and economic security policies. Tokyo has moved to increase defense spending to approximately 2 percent of its gross domestic product and has accelerated efforts to introduce long–range missile capabilities while reinforcing the defense of its southwestern islands. In addition, Japan has sought to acquire what it describes as a “counterstrike capability,” intended to deter potential attacks by enabling the ability to strike an adversary’s bases if necessary. These developments indicate that Japan’s security policy is shifting from a traditionally passive defense posture toward a more proactive deterrence strategy.

In the economic domain, Japan has also pursued policies aimed at reducing its dependence on China through supply chain restructuring. In strategic sectors such as semiconductors, batteries, and rare metals, Japan has expanded cooperation with the United States, Europe, and Southeast Asian countries to diversify supply chains, while recalibrating technology transfers and investment flows involving China. These measures demonstrate Japan’s growing emphasis on an integrated economic security strategy that links national security with economic policy.

As a result, China–Japan relations are increasingly evolving beyond a conventional diplomatic dispute into a structural rivalry encompassing military competition, economic and technological competition, and contestation over historical narratives. This transformation is likely to have significant implications for the broader security environment in East Asia, particularly as it intersects with the intensifying U.S.–China strategic competition centered on the Taiwan issue.

5. Implications and Policy Directions for South Korea

The deterioration of China–Japan relations and the resulting changes in the East Asian security environment carry important strategic implications for South Korea. Geographically situated at the center of Northeast Asia, South Korea maintains close relations with major powers including China, Japan, and the United States. Shifts in the regional strategic landscape therefore have the potential to directly influence South Korea’s foreign and security policies.

First, the strategic importance of the Taiwan issue is also gradually increasing for South Korea. The Taiwan Strait constitutes a critical maritime corridor for East Asian trade, and South Korea relies heavily on these sea lines for the import of energy and raw materials. In the event of a military conflict or maritime blockade in the Taiwan Strait, the South Korean economy could face significant disruptions. Moreover, if the United States and Japan were to become militarily involved in a Taiwan contingency, South Korea could face mounting pressure to make difficult strategic choices within the framework of the ROK–U.S. alliance.

Second, China–Japan tensions may also have significant implications for South Korea from the perspective of economic security. In contemporary international politics, the boundaries between security and economics have become increasingly blurred, with technological competition and supply chain restructuring emerging as central policy concerns. Strategic industries such as semiconductors, batteries, artificial intelligence, and critical minerals have become key arenas of interstate competition, developments that are likely to have substantial effects on South Korea’s industrial structure.

China remains one of South Korea’s largest trading partners, while Japan is also an important economic partner. The deterioration of China–Japan relations could therefore affect the supply chain configurations and trade environment faced by South Korean firms. Under these circumstances, South Korea may need to pursue strategies aimed at reducing excessive dependence on any single country while diversifying its supply chains. At the same time, safeguarding core industrial technologies and strengthening economic security policies will likely become increasingly important policy priorities.

Third, from the perspective of diplomatic strategy, South Korea will need to pursue a balanced approach. While South Korea's security policy is firmly anchored in the ROK–U.S. alliance, the country simultaneously maintains deep economic ties with China. Under such circumstances, excessive dependence on any single major power or the adoption of a one–sided strategic posture could constrain South Korea's diplomatic autonomy. South Korea therefore needs to maintain its alliance commitments while managing its relationship with China in a stable and pragmatic manner.

South Korea should also actively participate in regional multilateral cooperation. Addressing the diverse security challenges emerging in East Asia requires not only bilateral relations but also robust multilateral frameworks. Regional platforms such as ASEAN–led mechanisms, the East Asia Summit (EAS), and the Trilateral Cooperation framework among South Korea, China, and Japan can serve as important avenues for simultaneously promoting tension reduction and expanding practical cooperation.

Finally, South Korea will need to develop a long–term foreign policy strategy suited to the evolving international order. Strategic competition between the United States and China is likely to persist, and the strategic environment in East Asia will continue to undergo significant change. In this context, South Korea will need to formulate a comprehensive strategy that integrates security, economic, and diplomatic considerations in order to maximize national interests and enhance its strategic resilience.