Power & Security, Asia-Pacific Japan’s Response to a Chinese Invasion of Taiwan: A Four Year Outlook

In January 2024, the Center for Strategic and International Studies’ (CSIS) China Power Project published survey results of US and Taiwanese experts on China's invasion of Taiwan in relation to the Taiwan presidential election. The result showed a majority of both US and Taiwan experts assessed that a crisis is either likely or very likely in 2024. The crisis includes direct invasion of Taiwan as well as quarantine and blockade. As for the US intervention, a majority believe that the United States is unlikely to intervene in a contingency involving Taiwan’s remote islands, but likely in a high kinetic joint blockade or an invasion of the main island of Taiwan.

While expectations for US intervention are generally high, confidence in US allies and partners’ intervention is not high in all situations, from isolation to invasion. Even in the case of full-fledged invasion of the main island of Taiwan, 30 percent of US experts and 48 percent of Taiwanese experts say they have less or not at all confidence on the intervention. For experts in both countries, it is certain that Japan is on their minds.

However, as former Prime Minister Shinzo Abe said that the Taiwan contingency is a Japan contingency and a Japan-US alliance contingency, the Japanese strategic community generally believes that the Taiwan Strait contingency will spill over to Japan. As the Kishida Cabinet positioned China as "the biggest and unprecedented strategic challenge" on the 2022 National Security Strategy, there is a strong sense of caution toward China. Thereafter, the  government of Japan (GOJ) has substantially increased its defense budget for acquiring new defense capabilities by 2027, while strengthening the defense posture of the Nansei (Southwest) Islands. It is also true that not a small number of influential Liberal Democratic Party (LDP) lawmakers believe that Taiwan and Japan's security are closely related, as former Prime Minister Taro Aso hinted that a “survival threatening situation” (so-called right of collective self-defense) would be exercised in the event of a Taiwan contingency.

Four Drivers of the Japanese Government

There would be four drivers that motivate the GOJ to intervene in a Taiwan contingency: (1) Chinese government’s Taiwan policy, (2) US government’s Taiwan policy under the Taiwan Relations Act, (3) the US-China strategic nuclear power balance, and (4) geostrategic value of Taiwan to Japan.

China’s Taiwan Policy

The GOJ’s Taiwan policy is based on the Japan-China Joint Communiqué of 1972. The GOJ’s response in the event that China initiates a status quo change across the Taiwan Strait would be implemented in accordance with this joint communiqué.

The GOJ understood Beijing’s assertion that Taiwan is part of China, but this is only insofar as unification by the Beijing is carried out peacefully. In this context, it is considered that the GOJ has reserved the option to meet a situation that China attempts unification by non-peaceful means, such as coercive military means. In other words, in the event of a military invasion by China, the GOJ could stand by and watch, or it could intervene in the Sino-Taiwanese conflict in some way by deeming it an act of deviation from the Communiqué. In the latter case, the GOJ would not rule out responding to the Taiwan Strait crisis by military means.

The US government's Taiwan policy

The US government's Taiwan policy is the most significant driver. The US government is likely to militarily support the defense of Taiwan in accordance with the Taiwan Relations Act of 1979. President Joe Biden has stated repeatedly that he does not support Taiwan's independence but that America will fight to defend Taiwan. With considering that former President Donald Trump did not rule out defending Taiwan either, it is likely that there will be no major change in Taiwan policy no matter who wins the November 2024 presidential election in the United States.

Even if the United States does not directly participate in the war, the US military bases geographically available to support Taiwan are only in Japan and the Philippines. Prior consultation is required under the Japan-US Security Treaty when the United States uses the bases in Japan for military activities in Taiwan, but it is unlikely that the GOJ would refuse to consult with the United States, although not explicitly stated. In addition, if the US government requests Japan’s logistical support for the US military, the GOJ can certify an “important influence situation” and order the Self-Defense Forces (SDF) to provide supply, transportation, lodging, search and rescue, and other services to US military units. In the event of an attack on US military bases in Japan, the GOJ undoubtedly certifies an “armed attack situation” or “survival threatening situation,” and launch a defense operation, either independently or collectively with the United States.

Strategic Nuclear Power Balance

The US-China strategic nuclear power balance not only affects the credibility of US extended deterrence, but it also affects US defense support for Taiwan, just as the Biden administration was reportedly affected by Russian nuclear intimidation in Ukraine.

The implications are broad and complex. For example, in order to deescalate the situation, the United States could (1) hesitate to provide offensive weapons to Taiwan; (2) limit its support only to intelligence and logistical support; (3) not involve US forces in direct military operations, or (4) even discourage Taiwan authorities from attacking military targets in mainland China. There is also a possibility that the US government will ask the GOJ to refrain from supporting Taiwan authorities.

The most serious concern is that if US-China strategic nuclear forces reach parity in the 2030s, there will be an increased possibility that China believes that the United States is unlikely to intervene in a Taiwan contingency. An emerging "stability-instability paradox" greatly reduces the probability of a major war but increases the probability of a small-scale or indirect war between the two countries. In other words, China would be able to change the status quo in the Taiwan Strait through the skillful use of superior non-strategic nuclear weapons and conventional weapons.

Taiwan’s Geostrategic Value to Japan

 The fourth driver is Taiwan's geostrategic value to Japan. Japan and Taiwan are liberal democracies that share many values, strong economic ties, and close relations with millions of people coming and going annually. Taiwan is located at the convergence of maritime traffic in and out of the South China Sea, East China Sea, and Pacific Ocean. In addition, Taiwan, together with Japan, can act as a geographical barrier to control China's free access to the Pacific Ocean.

On the other hand, if China unifies Taiwan, China would have a base from which to expand its influence into the Pacific without obstacles, decisively altering the strategic balance in the western Pacific. In that case, China's naval and air power would restrain the deployment of US forces to the Western Pacific, and Japan would have to prepare for threats from the continental side and from the Pacific simultaneously. In other words, maintaining the status quo in Taiwan is a critical issue that directly affects Japan's survival and prosperity.

While the US government has intentionally kept its Taiwan policy ambiguous, the shifting US-China strategic nuclear power balance toward parity continues to add uncertainty to US Taiwan policy. In this strategic climate, Taiwan's geostrategic value would provide the basis for the GOJ to determine whether to intervene in Taiwan without being dragged down by the US policy.

Triangle Approach

Japan doesn’t have diplomatic relations with Taiwan due to historical factors since Japan's annexation of Taiwan in 1895. The GOJ has strictly adhered to the principle of non-governmental business exchanges and distanced itself from Taiwan. While diplomatic negotiations may have continued behind the scenes, exchanges between the two defense authorities ceased altogether.

If a Taiwan Strait crisis is to heighten in 2027, it will be necessary to find effective measures to improve the situation in a short period of time. However, it is impossible for Taipei and Tokyo to directly discuss military cooperation. A realistic approach would be an indirect one with the United States in the middle.

Given that two of the four drivers that motivate the GOJ to intervene in Taiwan are related to US Taiwan policy, the first possibility is Japan’s proactive involvement in US Taiwan policy.

For example, through policy discussions on the Taiwan contingency, the two governments could share situation awareness and the roles and missions in assumed situations. They could also discuss politically sensitive but crucially important issues, such as the timing of US stand-in forces’ prior deployment to the Nansei Islands.

As for information sharing between Japan and Taiwan, although it lacked speed, the Japan-US-South Korea triangle framework prior to the conclusion of the Japan-South Korea General Security of Military Information Agreement would be a useful reference.

While Japan's contribution regarding the strategic nuclear power balance is limited, the credibility of US extended deterrence can be enhanced if the United States, Japan, and South Korea achieve trilateral extended deterrence consultation and provide conventional support to the US nuclear forces cooperatively by Japan and South Korea.

In terms of military activities, if the SDF should organically integrate new defense capabilities such as counterstrike and standoff defense capabilities into the US defense posture, it could strengthen the US comprehensive deterrence capability.

The sharing of operational concepts could be achieved through Japanese observer participation in regular meetings of US and Taiwanese military authorities or by inviting Taiwan to multilateral joint exercises organized by US Indo-Pacific Command. A track two meeting with participation from Japan, the United States, and Taiwan could be utilized to discuss Taiwan-Japan military cooperation. A joint policy simulation involving lawmakers is expected to promote mutual understanding and sharing of issues related to political decisionmaking.