In December 2022, the Yoon Seok-yeol administration announced the South Korean version of the Indo-Pacific Strategy, “the Indo-Pacific Strategy for Freedom, Peace and Prosperity.” South Korea, as a pivotal country in the world, wants to project values of liberalism and solidarity into the Indo-Pacific region, presenting liberal democracy, rule of law, and human rights as universal values, aiming for a prosperous Indo-Pacific region and building trust among its people. The three major cooperation principles of reciprocity were declared. This is in line with the Biden administration's “Indo-Pacific Strategy” and contains a strategy to strengthen security cooperation between Korea, the U.S., and Japan, a core value alliance in Northeast Asia, amid intensifying competition for supremacy between the U.S. and China.

The war in Ukraine has emphasized the importance of the global value alliancés solidarity. Increasingly, the three countries of South Korea, the U.S., and Japan must cooperate in the interest of peace in Northeast Asia. In response to North Korea's nuclear threat and missile provocations, military exercises by South Korea, the U.S., and Japan have been limited to ballistic missile warning training, anti-submarine warfare training, and search and rescue training.

In October 2022, the U.S.-Japan joint exercise “Keen Sword” was conducted on Yonaguni Island in Japan, which cannot escape the impact of this sense of crisis. Yonaguni Island is located 110 kilometers from Taiwan and is at the forefront of U.S.-China security competition. Keen Sword , reflecting Japan's security anxiety over the possibility of China's invasion of Taiwan, is a large-scale joint exercise in which 23,000 members of the Self-Defense Force and 10,000 U.S. soldiers participated. Prior to this, in August of the same year, the Pacific Dragon Exercise was held to practice detecting and tracking North Korean ballistic missiles. With the participation of Korea, the U.S., and Japan as well as Canada and Australia, the target and scope of the exercise extended from Northeast Asia to the Pacific Ocean.

In January 2023, the Center for Strategic and International Studies (CSIS), a U.S. defense think tank, released the results of a war game analysis of the Taiwan invasion scenarios by China. The term “war game” refers to a strategy game in which two or more players command opposing armed forces in a realistic simulation of armed conflict (Dunnigan 1992).

Unlike the existing war game analysis of the Taiwan invasion scenarios, which focused on small-scale engagements at the tactical level, CSIS's analysis expands the scope to theater operations and includes three scenarios based on basic, optimistic, and pessimistic assumptions. It is different from previous studies in that it offers a quantitative analysis, such as battle damage assessments (BDA) on maritime forces and the results of U.S. air power engagements against China’s anti-access and area denial strategy (A2AD), obtained from 24 different simulations of the invasion scenarios (Cancian et al 2023).

In terms of security on the Korean Peninsula, there are divergent views among Koreans regarding the importance of the Taiwan issue. Some argue that it has little impact on the region's security. Others express concern about the possible ramifications of closer security cooperation between South Korea and Japan. Efforts to enhance cooperation have been hampered by unresolved historical issues, including forced labor, as well as concerns about Japan's rearmament.

The focus of my paper is to investigate the impact of a potential Chinese invasion of Taiwan on the security of the Korean Peninsula, and to explore the reasons why and how cooperation between Korea, Japan, and the U.S. could enhance security in the region. Specifically, I will use a war game simulation to demonstrate the importance of triangular security cooperation between these three countries.

One study that sheds light on the potential consequences of China's actions is the CSIS wargame, which has significant implications for defense, military, and foreign policy decision makers. The war game predicted that China would target U.S. air bases in Okinawa, Japan, in order to suppress U.S. military power projection towards Taiwan. This scenario underscores the importance of strong security cooperation between the U.S. and Japan in particular. Our discussion of the CSIS war game results will emphasize the importance of expanding security cooperation to Korea, the US, and Japan.

Based on the simulation conducted by the CSIS, a Chinese invasion of Taiwan would not achieve its intended strategic objectives. However, such a conflict would result in significant damage to all parties involved, including the United States, Taiwan, and Japan, with the war likely ending within three weeks. Therefore, to avoid another “pyrrhic victory,” it is imperative for South Korea, the U.S., and Japan to enhance their security cooperation and work towards an integrated regional security architecture that can effectively address the complex and evolving security challenges in the Indo-Pacific region. Such cooperation could help deter potential aggressors and promote regional stability, peace, and prosperity.

Why 2026 ?: CSIS postulated that China would invade Taiwan in 2026

Unlike China, which strengthened its military power based on continuous economic growth since the 1990s (See Figure 1), the U.S., which succeeded in establishing a unipolar global order after the Cold War, had to face domestic pressure to reduce defense spending (See Figure 2). In particular, as the war on terrorism began, the need for high-tech military capabilities was not great because the adversaries that the U.S. had to deal with were terrorists and rogue states. Furthermore, the pressure on the U.S. government to cut defense spending was mounting as the country bore the brunt of the 2008 global financial crisis. Meanwhile, as China emerges as a real threat rather than a conceptual concern, the Obama administration finally acknowledged that the U.S. military had not done enough to keep China's growing military power in check and it began modernizing six areas of the military including armor, artillery, air and missile defense, network, and individual combat systems. The battle domains, which were divided into land, air, and sea, have been expanded to multi-domain operations that cover space, cyber, and electromagnetics and the modernization of military capabilities began in 2019 and will not be completed until 2030 (U.S. Army 2019).

In 1996, when Taiwanese President Lǐ Dēnghuī' visited the United States, China raised the level of tension in the Taiwan Strait to the highest level by firing missiles into the waters near Taiwan and declaring a mobilization order in the Fujian region. However, when the United States dispatched an aircraft carrier under the 7th Fleet to Taiwan, China showed signs of giving in to the powerful naval power of the United States by stopping missile provocations and withdrawing the mobilization order. Since then, China has invested a huge amount of defense spending to modernize its maritime power and dramatically enhance its anti-ship, anti-aircraft, and anti-submarine capabilities while swallowing its pride (Porch 1999).

CSIS judges the year 2026 as the best window of time to invade Taiwan as the military power gap between the U.S. and China is at its narrowest point before the U.S. military modernization program is completed. With President Xi Jinping’s ambition to serve for the fourth consecutive term in 2027 (Chen et al 2022), he is likely to regard 2026 as the last opportunity to invade Taiwan. In other words, if China misses the opportunity in 2026, China may have to wait for another 100 years for the next opportunity.

Why would China attack Japan?

While many of the NATO countries offered stable supply bases to the U.S. during the war in Ukraine, the U.S.’s options would be limited to Japan, South Korea and the Philippines in the event of war in Taiwan. Of these countries, the biggest eyesore for China would be Japan as it will serve as a strategic supply hub for the U.S. In particular, if the U.S. Air Force stationed in Okinawa is not suppressed, China will inevitably suffer damages to its maritime and landing forces, which play a decisive role in the invasion of Taiwan. China will try to limit the sortie of the U.S. Air Force through a missile attack on the Okinawa base in Japan to lay the groundwork for successful amphibious operations at the beginning of the war.

As a first step towards success, it is imperative for China to execute landing quickly, block the deployment of U.S. reinforcement to Taiwan, and contain waters contiguous to Taiwan. CSIS estimates that China’s People’s Liberation Army (PLA) will land somewhere between 22,000 to 43,000 troops in Taiwan (See Figure 3), but its success would be contingent on its ability to suppress the U.S. Air Force in Okinawa (Cancian et al 2023).

Would the U.S. attack mainland China?

It is difficult to predict with certainty what actions the U.S. would take in the event of a conflict with China, as this would depend on a variety of factors such as the nature of the conflict, the goals of both parties, and the political and strategic considerations involved.

In this war game, the U.S. did not launch an attack on mainland China to avoid an all-out war with China. This is to avoid escalating into a nuclear war by confining the theatre to Taiwan’s territorial waters and land. Therefore, the United States did not strike naval facilities and A2AD bases on the mainland where Chinese warships are anchored, despite suffering enormous damage in the war game (See Figure 4).

China can mobilize up to 2 million troops in wartime and the only weapon system to respond to this massive manpower is nuclear weapons, so the United States, which does not want to escalate the war into a nuclear one, has little intention to launch an attack on the Chinese mainland. Just as the U.S. avoided the use of nuclear capabilities during the Korean War, it is very unlikely for the Biden administration to take the nuclear option or attack mainland China in the event of an invasion of Taiwan.

What is North Korea’s role in China’s invasion of Taiwan?

There is growing concern among experts that China could force the U.S. to fight on two fronts by inducing North Korea to launch localized provocations at the same time as they invade Taiwan.

The CSIS war game scenario assumed that 50% of the U.S. Air Force stationed in South Korea would be committed to counter-invasion operations in Taiwan, but North Korea’s provocation would likely keep the United States Forces Korea (USFK) from being diverted to Taiwan. In this case, the U.S. could fall into a trap of having to deal with two nuclear powers at the same time. The Nuclear Posture Review 2022 also forewarned of the possibility of simultaneous provocations in Taiwan and the Korean peninsula.

In the Ukraine War, Russia, Belarus, China, and North Korea demonstrated solidarity under the banner of proletarian internationalism. In particular, to help Russia with its ammunition shortage, North Korea covertly provided ammunition, which North Korea denied but the U.S. refuted with video evidence (Cha 2022). In accordance with the treaty of the China-North Korea alliance signed in 1961, North Korea is likely to provoke South Korea to prevent the deployment of USFK forces to Taiwan.

Battle Damage Assessment in the event of China’s Invasion of Taiwan

Looking at the BDAs revealed in the war game, the United States lost 17 ships including two aircraft carriers, Japan lost 26 battleships, and China lost 138 battleships. The relatively large damage inflicted on the Chinese battleships can be attributed to the U.S. Air Force’s intense strikes from the beginning of the war (see Table 1).

However, the U.S. also suffered enormous damage on its aircraft as a result of China’s powerful A2AD capabilities. The U.S. and Japan suffered overwhelmingly high fighter jet losses compared to China due to China’s surprise attacks on U.S. military bases in Japan and U.S. aircraft carriers. On the other hand, the U.S. did not attack aircraft on mainland China, so fighter jet losses were relatively larger for the U.S. As a result, when a conservative scenario was applied, it was analysed that China failed to achieve its strategic goal within 21 days of the start of the war, but the United States and Japan would also suffer enormous damage.

Defeating China's desire to invade Taiwan and foiling their strategic objectives can be accomplished by implementing four basic premises.

Taiwanese people’s will to fight is most critical

When the war in Ukraine broke out, most experts expected that Russia would bring the war to an end rather quickly. However, the people of Ukraine proved such prediction wrong with their strong will to fight. When Crimea was annexed by Russia in 2014, Ukraine did not show any particular signs of resistance, which taught Putin a very wrong lesson (Kofman 2017).

However, in the current war in Ukraine, the Ukrainian people were reminded of the lesson that their silence when Crimea was lost to Russia in the past did not result in lasting peace for Ukraine. Above all, thanks to the political leader’s courage and will to fight, the people of Ukraine fiercely resisted against the relentless attack of Russia, and were finally able to turn the tide and restore the current frontline. Some have doubts about whether the Taiwanese people will resist Chinese invasion while enduring as many sacrifices as the Ukrainians did.

Taiwan has a notable history of democratic governance and a strong sense of national identity. The Taiwanese people have demonstrated their resilience and determination in confronting various challenges in the past, including the martial law era and the devastating 921 earthquake. Moreover, Taiwan has a well-trained and well-equipped military, and the government has increased its investment in defense and security in recent years to respond to the rising military presence of China in the region. For a war game result in which the strategic goal of China’s invasion of Taiwan fails in a maximum of 21 days, the Taiwanese people’s determination to defend their land is a prerequisite, which would render the CSIS war game meaningless if not met.

U.S.’s Ukrainian response would not work

The United States must be willing and able to provide military support to Taiwan, including the deployment of significant military forces and the use of advanced weapons systems. The U.S. and NATO allies chose to supply weapons and ammunition instead of being a belligerent to the war to support Ukraine, which would not be a viable option to defend Taiwan from China’s invasion. This is not just due to the military power gap between China and Taiwan.

NATO allies around Ukraine can serve as a reliable supply base for the ongoing war. However, Taiwan, an island floating in the middle of the sea, is in a different geopolitical situation. Once China’s military forces overwhelm Taiwan and successfully land on the island, it would be nearly impossible to create conditions to overturn the situation. Meanwhile, for the U.S., if the waters off Taiwan are blocked, the supply route for the sustainment of operations will be cut off, making it more difficult to defend Taiwan. China would try to devastate Kadena Air Base in Okinawa with massive missile attacks from the beginning of the war. The Chinese will immediately launch an amphibious operation in Taiwan, and enter a naval blockade to cut off U.S. reinforcements. Therefore, the U.S. cannot afford to delay military intervention as it did in Ukraine. If the U.S. hesitated and missed the golden time for military intervention, China would quickly end the operation.

The Triangle Security Cooperation is essential to Taiwan's defense

Japan and South Korea must be willing to cooperate with the United States to provide significant military support to Taiwan, including the use of their own military forces and advanced weapons systems. CSIS’s war game also assumes that the U.S. Navy and Air Force will secure stable bases from which they can conduct sustainable operations. The U.S. could use assets in the Philippines and South Korea, but Kadena located in Japan would still be the most significant in dealing with the Taiwan situation (see Figure 5). If U.S. bases in Japan are irreparably damaged by China’s missile attacks, the U.S. and Japan would never be able to win the war even by a narrow margin.

Based upon a base scenario that is neither optimistic nor pessimistic, 37 battalions of the People’s Liberation Army would successfully land on Taiwan and 30 battalions with 30,000 troops would gather on the coast. With stable bases secured in Japan, the war would end in 14 days with U.S. air strikes, but if Japan’s military base is destroyed and its function is lost, landing of the Chinese PLA forces wouldn’t be deterred and it cannot be asserted that the war will end in 14 days (See Table 2).

Chinese fleet must be subdued at the start of war

The Chinese fleet must be subdued at the start of the war to prevent it from gaining control of the Taiwan Strait and cutting off Taiwan's access to the outside world. The most effective way for the U.S. to thwart China’s invasion of Taiwan is to use air-to-ship missiles to first subdue Chinese naval vessels outside the Chinese mainland defense zone. In this war game, although Aegis ships responded very well against China’s missile attack, they were unable to intercept all missiles heading to Taiwan. This is despite the fact that the Aegis ships had powerful missile defense capabilities. It appears from the war game results that China’s A2AD power is stronger than the U.S. estimated. Fighter jets with strong stealth capabilities such as F-35s have also suffered serious damage (See Table 3).

In the end, in order to stop the landing operation without destroying the missile bases and A2AD forces installed on the Chinese mainland, the U.S. has no choice but to rely on air-to-ship missiles that can strike from a long distance outside the Chinese mainland defense zone.

The National Defense Authorization Act (NDAA), signed by President Biden on December 24, 2022, contains a total of 4,409 pages, of which 3,100 are devoted to investments in the Indo-Pacific region in order to gain a competitive edge over China (US Congress 2023). In an effort to reorganize the U.S. alliance in the Indian Pacific region, the Biden administration is attempting to integrate the military assets and capabilities of like-minded countries. Unlike NATO’s collective security system, the U.S. Asia-Pacific region security system is based on bilateral treaty alliances and can be described as a hub-and-spoke model. The Biden administration is now working to transform the Indo-Pacific strategy into a collective security system like NATO by implementing integrated security, backed by like-minded regional powers (White House 2022). It was difficult for countries in the past to build a unified security system due to historical sediments, territorial disputes, and competition between countries. This led the U.S. to adopt a hub and spoke system.

However, as the U.S. faces a situation where its capacity and willingness to maintain a liberal order is no longer the same as before, it is carving out a full-fledged integrated security system between its allies in the Indian and Pacific oceans. In addition, in a situation where it is difficult for the U.S. to project 100% of its power in the Indo-Pacific region due to Russia’s invasion of Ukraine, it is also working to expand the spatial scope and role of NATO to the Indo-Pacific region. As part of the revised U.S. security strategy, South Korea, the U.S., and Japan must enhance cooperation for stability in the Indo-Pacific region. CSIS war game simulation results provided a highly quantitative and probable analysis compared to previous studies when looking at assumptions, premises, and analysis methods.

It is crucial to recognize that the conclusions drawn from the analysis undertaken by CSIS rely on certain assumptions, which have been subject to various criticisms. Therefore, it is necessary to approach the findings of the study with a measure of caution. Moreover, it is possible that the CSIS researchers may have overstated the threat in order to boost defense spending and rally regional allies around the U.S. Indo-Pacific strategy. Assuming, however, that the premises presented by CSIS are valid, there are legitimate apprehensions about China's potential to launch attacks on Japan and to pressure North Korea to carry out provocations as a means of deterring the deployment of US forces to Taiwan. These issues serve to illustrate that the Taiwan issue is not exclusively a concern for the United States, but also for other regional powers.

In response to North Korea's nuclear threat and missile provocations, efforts are underway between South Korea and Japan, led by the United States, to foster security cooperation. Furthermore, the growing possibility of China invading Taiwan has underscored the need for security cooperation among Korea, Japan, and the United States. South Korea and Japan have had strained relations for the past five years over apologies and compensation for the past. According to Japanese participants at the Trans Pacific Dialogue (TPD) South Korea-Japan Special Session held in December 2022, “South Koreans are curious about why Japan does not apologize for its past history, and they are also puzzled by the fact that the standard of compensation for victims of past history changes according to who is in power at the time.” Since these different perceptions of South Koreans and Japanese cannot be bridged and are running parallel to each other, President Yoon is pursuing a comprehensive resolution of historical conflict issues. This includes a decision on forced labor compensation issues. In addition, the Yoon Seok-yeol administration is also taking positive steps towards strengthening security cooperation between Japan and South Korea. In light of changes in the international security environment, the Kishida administration is also cognizant of the importance of improving South Korea-Japan relations. Prime Minister Kishida stated, “We will resolve the pending issues and return them to a sound state.” This could be an indication that South Korea-Japan relations will soon improve (Jang 2023).

When asked about the possibility of ROK-US-Japan security cooperation in a situation where North Korea's nuclear threat is escalating, the majority (71.9%) of respondents gave a positive outlook. This indicates that the public's perception of the South Korea-Japan relationship has changed since the inauguration of the Yoon Seok-Yeol administration. The Russian invasion of Ukraine and the escalating conflict between China and Taiwan brought about changes in the international situation. This led to a change in public opinion about South Korea, the U.S., and Japan's need for trilateral security cooperation. In addition, when asked, “Do you know about the South Korean government's response strategy to the North Korean nuclear threat?” 61.6% of the respondents answered that they did not know the government's response strategy. Lack of understanding of the government's strategy prompts anxiety about security and leads to a debate about the redeployment of US tactical nuclear weapons. This debate also leads to the argument for independent nuclear armament (Chey 2023).

In a situation where North Korea’s nuclear threat is growing more sophisticated and its missile threat continues, for early detection and warning, it is necessary to share information through integrated management of surveillance assets between South Korea and Japan. If an all-out war breaks out on the Korean Peninsula, cooperation to sustain operational support from Japan, where the United Nations Command’s rear bases is located, must also be strengthened. It seems to be abundantly clear why security cooperation between South Korea, the U.S. and Japan must change, evolve, and develop in line with the changing security reality.

If China were to successfully invade Taiwan, it would have far-reaching consequences for the balance of power in the region and the interests of the U.S. and its allies. Taiwan is a critical node in the U.S. Indo-Pacific strategy, and a major partner for Japan and South Korea in trade and security cooperation. An invasion by China would severely damage the interests of all these countries and threaten their security and economic stability. As a result, the U.S. has a strong interest in supporting Taiwan's defense against any aggression from China. The U.S. has long-standing security commitments to Taiwan and has sold arms to Taiwan to help it maintain a credible defense against potential Chinese aggression. In addition, the U.S. has sought to strengthen security cooperation with its regional allies, including South Korea and Japan, to deter China and enhance regional security. For South Korea and Japan, the situation in Taiwan also has significant implications. Both countries are major trading partners with Taiwan and rely on its technology and expertise for their own economic and security interests. In addition, South Korea and Japan are important U.S. allies in the region and would be directly impacted by any conflict in the Taiwan Strait.

In light of these factors, South Korea and Japan have a strong interest in working with the United States to prevent any conflict in the region and to maintain stability and security. This includes supporting Taiwan's defense efforts, enhancing regional security cooperation, and working with the U.S. to deter any aggression from China.