The United States and Japan Should Prepare for Chinese Aggression Against Taiwan

As China continues to increase its pressure against Taiwan, the questions of whether it will eventually use force to bring Taiwan under its control and how the United States should address this issue have moved to the center of the U.S. foreign policy debate. An often overlooked but critical factor is the extent to which any U.S. response to Chinese aggression would require the use of its forces in Japan and significant Japanese operational and logistic support. In the face of growing Chinese military capabilities and weakening deterrence, the United States and Japan need to make preparing for a conflict in the Taiwan Strait a top priority for the alliance. How well the United States and Japan are able to deter an attack on Taiwan and respond jointly and effectively to Chinese aggression if deterrence fails could determine Asia’s future, as well as their own.

There is a growing recognition in Japan that a Chinese occupation of Taiwan would fundamentally challenge its security. If China were to station People’s Liberation Army (PLA) forces on Taiwan, its military would be only 110 kilometers from Yonaguni Island, Japan’s westernmost point. Such an outcome would render it far more difficult for Japan to defend Yonaguni, the Senkaku/Diaoyu Islands, and Okinawa. Given that China views the Senkaku/Diaoyu Islands as a part of “Taiwan Province,” China could attempt to seize them during a conflict over Taiwan. If China achieved its objectives in spite of U.S. intervention, Japan would see its ally severely weakened, which would force it to fundamentally reconsider its foreign policy and defense posture.

A successful Chinese annexation of Taiwan would also undermine Japan’s economic security. Taiwan is Japan’s fourth-largest export market, and should China control Taiwan, it would be able to curtail Japan’s access to that market. Over 40 percent of Japan’s maritime trade passes through the South China Sea; with control over Taiwan and its military installations throughout the South China Sea, China would be in a position to force shipping bound for Japan to take more inefficient routes, hurting Japan’s economy. In addition, China would presumably gain control of Pratas Island (currently administered by Taiwan), a strategic island adjacent to the entrance to the South China Sea from the Philippine Sea, further cementing its hold on this critical maritime artery. Finally, given Taiwan’s proximity to the approaches to Japan’s ports, during wartime China could threaten Japan’s import-dependent economy.

Faced with this potentially dire scenario, Japanese leaders have begun to link Taiwan’s security with Japan’s, which would enable the country to play a role in Taiwan’s defense. This past June, Japan’s defense minister stated “the peace and stability of Taiwan is directly connected to Japan.” One month later, Japan’s deputy prime minister argued that “if a major problem took place in Taiwan, it would not be too much to say that it could relate to a survival-threatening situation.” Such assessments would enable Japan to respond to a Chinese attack on Taiwan under the auspices of exercising collective self-defense.

Japanese prime minister Fumio Kishida has not gone this far but has argued that “the front line of the clash between authoritarianism and democracy is Asia, and particularly Taiwan,” and that Japan “cannot respond except by cooperating with our ally, the United States.” Former Prime Minister Shinzo Abe has gone the furthest to date, declaring in November, “A Taiwan emergency is a Japanese emergency, and therefore an emergency for the Japan-U.S. alliance. People in Beijing, President Xi Jinping in particular, should never have a misunderstanding in recognizing this.”

The United States and Japan have also begun to signal that preparing for a conflict in the Taiwan Strait is becoming a greater priority for the alliance. In April 2021, for the first time in five decades, the two countries included a clause on Taiwan in their leader-level joint statement. Two weeks ago, during a meeting between the U.S. secretaries of state and defense and their Japanese counterparts, the two sides “underscored the importance of peace and stability in the Taiwan Strait” and “resolved to work together to deter and, if necessary, respond to destabilizing activities in the region.”

Strong statements notwithstanding, there remain questions regarding what level of support Japan would offer the United States during a conflict. Critically, at a minimum the United States would need to use it forces on Japan, but doing so would require prior consultation with Tokyo. This mechanism has never been invoked, and it could delay a U.S. military response with significant operational consequences.

It is also unclear how much Japan would be willing to actively assist the United States. According to its constitution, Japan could only offer its broadest support, such as ballistic missile defense, anti-submarine warfare, and combat operations alongside the United States, if it views a Chinese attack as representing a “survival-threatening situation.” While at first glance it might seem as though an attack on Taiwan would not meet this threshold, a Chinese takeover of Taiwan could be seen as posing a danger to Japan’s survival given its proximity to Japanese territory. In addition, the government’s advisory panel argued that a “survival-threatening situation” should include one in which “not taking action could significantly undermine trust in the Japan-U.S. alliance” or “the international order itself could be significantly affected.” A failure to assist the United States in coming to Taiwan’s defense could be seen as fatally weakening the U.S.-Japan alliance. Given Kishida’s statement that Taiwan is the front line of an ideological competition between democracy and authoritarianism, Japan could also be coming to the view that a Chinese attack would be considered a threat to international order.

The deep pacifism among Japanese citizens and potential costs associated with assisting the United States could also limit Japan’s support. If Japan were to allow the United States to use bases in Japan to conduct operations in defense of Taiwan, those bases could come under attack, and China could also choose to target Japanese assets supporting U.S. operations. China is Japan’s largest trading partner and could retaliate by significantly curtailing bilateral trade and attempting to interdict critical shipments of oil and gas to Japan. China would also likely pressure Japanese businesses operating on the mainland and encourage a nationalist backlash against Japanese goods.

As I argue in a new paper, it is critical for the United States to establish an understanding of how Japan is likely to respond to an unprovoked attack on Taiwan and the type and degree of support Tokyo would be prepared to offer Washington. The fact that Japan would bear significant costs for supporting U.S. operations makes it even more important for the United States and Japan to prioritize genuine and regular consultations that focus on what the United States would need in order to defeat Chinese aggression and how it can address any Japanese concerns. These critical discussions need to occur now, as there would be limited time to respond to a Chinese attack and any delay could significantly hamper operations or even make a defense of Taiwan unfeasible.

After gauging the level of likely Japanese support, the United States should work with Japan to determine which operational challenges Japan can most effectively help the United States overcome within those parameters. The allies should then adapt elements of the alliance relationship to maximize their ability to respond quickly and effectively to Chinese aggression against Taiwan.

First, the United States should work closely with Japan in developing capabilities that enhance Japan’s defense and would have the added benefit of contributing to the defense of Taiwan. This would include integrating intelligence, surveillance, and reconnaissance capabilities, assisting Japan’s development of cutting-edge military capabilities, and urging Japan to increase its defense spending and rapidly modernize its forces.

Second, the United States should take steps that facilitate the use of U.S. forces in Japan and Japanese assets even if Japan chooses not to directly assist U.S. operations. Specifically, the allies should work together to create conditions for smooth prior consultation, while the United States should implore Japan to publicly state that an attack on U.S. forces in Japan would be considered an attack on Japan itself.

Third, the United States should coordinate with Japan to enable Tokyo to more effectively support U.S. operations if it chose to do so. Priorities should include transforming command and control in Japan, addressing resupply challenges, and positioning additional ammunition and critical supplies in Japan.

Finally, the United States should enhance Japan’s ability to directly intervene in the defense of Taiwan. This would entail leveraging Japan’s western islands, encouraging and facilitating Japan’s establishment of a joint warfighting headquarters, developing a plan with Japan to help it counter Chinese economic and political retaliation and resist Chinese pressure, and facilitating military-to-military communication between Japan and Taiwan.

To prevent a war that would be ruinous for the United States, Japan, Taiwan, and China, the United States and Japan should urgently increase their coordination and preparation for a Taiwan conflict. Deterring Chinese aggression against Taiwan and developing and fielding with urgency the capabilities necessary to respond to a Chinese attack should animate all conversations among the countries’ national security leadership. The regional order that has preserved peace and stability in the Indo-Pacific for the past three-quarters of a century hangs in the balance.

For more on this topic, see David Sacks’s discussion paper, “Enhancing U.S.-Japan Coordination for a Taiwan Conflict.”