The long-simmering issue of Taiwan’s international status is the most likely trigger for conflict between the United States and China. Given the increase in China’s military might over the previous decade, the willingness of the United States’ allies to aid efforts to defend Taiwan are paramount. Most critical is the extent to which Japan would commit military forces alongside the United States.
Recent wargames show the United States would be hard-pressed to win a conflict over Taiwan without Japan’s support.1 To be sure, Japan has significant interest in maintaining peace and stability in the Taiwan Strait, as then–Prime Minister Yoshihide Suga stated for the first time in April 2021, standing alongside President Joseph Biden.2 However, the post–World War II legacy of pacifism remains a powerful force in Japanese domestic politics and could limit Japan’s willingness to commit the Japan Self-Defense Force (JSDF) to combat operations during a Taiwan contingency.
There is evidence that parliamentary, coalition governments such as Japan’s are more receptive to public pressure in foreign policy than other democratic systems, which is a vital consideration when coupled with the domestic hesitation to use the JSDF outside of the direct defense of Japan.3 Given the high stakes of this potential conflict, Washington should work through diplomatic and military channels to ensure Japan’s commitment to the defense of Taiwan if the United States decides to intervene.
The U.S. Alliance Structure and the Question of Taiwan
Changes to Japan’s defense policy over the previous decade have led some to assume the country would intervene in a Taiwan conflict. Most of the discourse centered on the 2015 reinterpretation of the Japanese constitution to permit collective self-defense and Prime Minister Fumio Kishida’s recent announcement that the nation would increase defense spending by two-thirds over the next five years.4 Starting with the decision on collective self-defense, some have interpreted this as Japan “pulling free from its self-binding constraints and restoring an activist foreign policy.”5 However, collective self-defense does “not establish a legal basis for the SDF to be deployed on combat missions abroad.”6 The situation must meet three criteria for force to be authorized under collective self-defense: An attack is a direct threat to Japan’s survival; armed force is the only appropriate means to protect Japan; and the minimal amount of force necessary to defeat the threat is used.7
Even if the criteria were met, it is not clear the Japanese public would permit the JSDF to respond in tandem with the U.S. military. This is a serious consideration because public opinion in Japan shows there is hesitancy to either directly or indirectly provide military support in defense of Taiwan. Though 85 percent of the public views the U.S.-Japan alliance favorably, support is much lower for assisting the U.S. military in defense of Taiwan.8 Only 40 percent support providing logistics support to the United States in noncombat zones; 27 percent support provisioning weapons or ammunition in noncombat zones; 20 percent support supplying weapons and ammunition to U.S. forces in combat zones; and a dismal 15 percent support fighting alongside U.S. forces.9 While the Japanese public supports government efforts to modernize and expand the JSDF, this does not necessarily mean Japan has become more willing to use military force in a Taiwan contingency.
Japan’s and the United States’ “One China” policies are similar, leading many observers to assume that Japan’s response to a Taiwan contingency would therefore be in lockstep with that of the United States. Tracing back to the normalization of relations with Beijing in the 1970s, both recognized the People’s Republic of China as the legal government of China but not its “claim of sovereignty over Taiwan.”10 Rather, the United States adopted the “Japan Formula,” which established official relations with Beijing but maintained Washington and Tokyo’s right to “practically significant, if ‘unofficial’ and ‘non-governmental,’ engagement with Taipei.”11 This framework has remained the guiding principle for how the U.S.-Japan alliance has managed relations with China and Taiwan.
The U.S.-Japan Security Treaty is unique among U.S. treaty alliances because it is not a mutual defense treaty. Unlike NATO’s Article V declaration that “an armed attack against one or more [member] . . . shall be considered an attack against them all,” the U.S.-Japan alliance was designed to protect Japan from external aggression.12 Article V of the U.S.-Japan Security Treaty obligates a U.S. response only after an attack on allied forces “in the territories under the administration of Japan,” while Article VI grants the United States access to bases in Japan with the stipulation that “the U.S. would engage in ‘prior consultation’ with Japan” before committing its forces to combat operations abroad.13 The treaty is essentially “a trade of [Japanese] bases for [American] security protection.”14 Therefore, there is no obligation for a bilateral response to a conflict over Taiwan that does not involve a concurrent attack on allied forces in Japan.
Principally, the main problem for the United States is that the Japanese government has committed to expanding the JSDF and acquiring new capabilities that could help prevent a conflict over Taiwan while simultaneously failing to signal to China that the JSDF could be a potential adversary in a contingency. Prime Minister Kishida announced his plan to increase the JSDF’s budget from $46 billion to roughly $64 billion by 2027.15 As part of this expansion, the JSDF is pursuing upgrades to the Type 12 antiship missile to increase its range from 120 to 620 miles, acquiring 400 Tomahawk land-attack missiles, equipping its fleet of diesel submarines with vertical launch systems, and jointly researching hypersonic missile defenses with the United States.16
In all, the JSDF is undergoing an extensive qualitative upgrade to its power-projection capabilities. But these changes are primarily intended to bolster the ability of the JSDF to defend Japan, not to project force within the region. For example, after announcing the acquisition of Tomahawks, Prime Minister Kishida prohibited their use in preemptive or offensive strikes in keeping with the spirit of Japan’s constitution.17 To some extent, Japan’s constitution and domestic policies undercut the deterrent value of the JSDF’s upgrades.
Japan’s Interests in Taiwan
Despite the constraints on Japan committing the JSDF to a conflict over Taiwan, the United States has meaningful leverage to convince the Japanese public of the necessity of maintaining the Taiwan status quo—namely, China represents a major challenge to Japan’s security; Japan has its own national interests in maintaining peace in the Taiwan Strait; and the U.S.-Japan alliance is viewed as the foundation of Japan’s security policy. The importance of Taiwan to regional stability and the United States’ importance to Japan’s own security create a strong link between Japan and Taiwan that is often left unspoken.
The modernization and expansion of the JSDF has largely been driven by China’s assertive behavior in the East China Sea since the early 2010s. In 2012, Hu Jintao declared the Communist Party would “build China into a maritime power,” and, in the ensuing years, Xi Jinping doubled down on this commitment to “step up efforts to build China into a strong maritime power country” and to complete the People’s Liberation Army’s (PLA’s) modernization by 2035.18 These were not hollow words. In 2004, the PLA’s budget surpassed that of the JSDF. Tensions escalated around the Senkaku Islands in 2010 after the Japan Coast Guard arrested the crew of a Chinese fishing vessel, which led to a series of events that resulted in continual PLA Navy (PLAN) and China Coast Guard presence around the Senkakus that continues to this day.19 While the United States’ primary concern in the region has been the status of Taiwan, the JSDF has engaged with the PLA elsewhere, and Japan’s military modernization is not necessarily intended to deter China from invading Taiwan.
Even so, Japan has strategic, economic, and political ties with Taiwan the United States could use to encourage Japan’s assistance in deterring a conflict. There is concern in Tokyo that, were China to gain control over Taiwan, it would allow the PLA to operate more freely in the western Pacific and around the Japanese Home Islands.20 On the economic front, Taiwan is Japan’s fourth largest trading partner, contributes more foreign direct investment to Japan than China, and is a major source of advanced semiconductors crucial to Japan’s high-tech economy.21 Trends show that Japan-Taiwan economic ties have been strengthening while China-Japan ties have stagnated or even weakened over the previous few years.22 Finally, 80 to 90 percent of the Japanese public consistently expresses a negative view of China.23 Therefore, with the United States being critical to Japan’s own security and Japan being vital to U.S. efforts to defend Taiwan, Japan has a vested interest in supporting the defense of Taiwan and deterring China.
Convincing Japan’s government is not enough, however. Take, for instance, Japan’s involvement in a United Nation’s peacekeeping operation in Sudan. In a 2016 incident, “the JSDF encountered serious exchanges of fire” with forces in South Sudan, which was the first time the JSDF risked combat casualties abroad. In response, the public called for its immediate withdrawal from Sudan, and the popular Prime Minister Shinzo Abe committed “to resign if any JSDF personnel were killed.”24 Now, imagine the domestic opposition that would arise if Japan considered intervening in a Taiwan conflict that could result in hundreds or thousands of casualties. U.S. officials must convey to their Japanese counterparts and the Japanese public that Japan’s assistance in a Taiwan conflict is necessary not only for success, but also for the credibility of the U.S.-Japan alliance, and therefore the stability on which Japan relies.
The United States has moved Japan toward a more activist foreign policy in the past. During the first Gulf War, the Bush administration sought Japan’s participation in the international coalition to remove the Iraqi Army from Kuwait. But, citing the restrictions in its constitution, Japan did not contribute forces until after the conflict ended, when the JSDF belatedly dispatched minesweepers to the Persian Gulf. Instead, it contributed funds to the operation, which was widely derided as “checkbook power.”25 However, in the wake of the 9/11 attacks, Japan quickly assigned forces and sent JSDF units to Afghanistan, although they were kept in noncombat roles.26 Both these examples provide a cautionary tale for Taiwan, as Americans’ expectations of what Japan would contribute likely exceed what it may actually offer in response to a Chinese invasion or blockade of Taiwan.
What the United States Should Do
Removing Japan’s domestic limitations on the use of military force is something only the Japanese public can undertake. However, the United States must encourage changes to Japan’s domestic environment and ensure JSDF support to the U.S. military in the event of conflict. The likelihood of Japan participating in a Taiwan contingency has moved in a favorable direction in recent years, but the needle needs to keep moving—with urgency. Following the Biden administration’s emphasis on integrated deterrence in the 2022 National Security Strategy, the following are efforts the United States should undertake to enhance allied deterrence in the Taiwan Strait:27
• Former Japanese government officials have stated an invasion of Taiwan “could be a situation posing a threat to Japan’s survival,” which could warrant a military response from the JSDF under collective self-defense.28 U.S. diplomats should ask Japan to officially state its belief that a Chinese invasion of Taiwan may be a “survival threatening” situation for Japan, which enhances the likelihood of an allied response. This would not be a firm commitment for Japan to defend Taiwan but would increase its likelihood, similar to the current U.S. policy of strategic ambiguity.
• To meet the terms of the U.S.-Japan Security Treaty, the United States should engage in “prior consultation” with Japan on the use of military facilities in a Taiwan emergency. If this discussion has taken place, it should be made public, as a secret deterrent effort has no chance of success.
• Through the Indo-Pacific Economic Framework for Prosperity or Comprehensive and Progressive Agreement for Trans-Pacific Partnership, the United States and Japan should work to further integrate Taiwan into the international economy.29 This would reduce Taiwan’s economic dependence on China and bolster domestic efforts to fund self-defense.
• The alliance should pursue a joint command-and-control organization to ensure unity of effort in a Taiwan conflict, as there is no existing bilateral structure.30 This is the next logical step following the announcement of the formation of the Japan Joint Operations Command and the United States’ reorganization of U.S. Forces Japan to Japan Joint Force Headquarters.
• The Japan Maritime Self-Defense Force has not conducted a Taiwan Strait transit alone or alongside other nations.31 The United States has started to lead multinational transits of the Strait, and the U.S.-Japan alliance should conduct bilateral transits as a display of allied resolve.32
• The U.S. military and JSDF should coordinate deployments along the Ryukyu Islands to create an antiaccess/area-denial strategy. Japan controls one of two choke points the PLA would need to traverse to operate on the eastern side of Taiwan, and thoughtful placement of JSDF assets would free U.S. forces to operate in other areas.33 This would make a Taiwan invasion or blockade riskier for the PLA and less likely to succeed, while adding combat capability to the fight without the United States having to acquire new platforms or systems.
To deter China from invading Taiwan, the United States needs support from allies and partners, as its globally dispersed military is faced with a constantly expanding regional power. The Biden administration’s National Security Strategy recognizes this and states that “allies and partners . . . add significantly to our own strengths.”34 But this is only the case if U.S. allies such as Japan are willing and able to use their strengths to complement those of the United States.
When it comes to maintaining peace in the Taiwan Strait, it is not readily apparent that Japan will support the United States to the extent that may be necessary for success because of the constraints of Japan’s constitution, the asymmetric nature of the U.S.-Japan Security Treaty, and the Japanese public’s reluctance to support the use of force. However, the alliance can, and must, work through these limitations. Because of recent efforts to expand and modernize the JSDF, ensuring Japan’s participation in a Taiwan contingency would improve the effectiveness of allied deterrence by significantly complicating the PLA’s operational environment and reducing the likelihood of its success. If deterrence should fail, then the U.S.-Japan alliance would be much better equipped and capable of defeating an invasion or blockade of Taiwan than the United States by itself.
1. Mark F. Cancian, Matthew Cancian, and Eric Heginbotham, The First Battle of the Next War: Wargaming a Chinese Invasion of Taiwan (Washington, DC: Center for Strategic and International Studies, 9 January 2023), 3; and Stacie Pettyjohn, Becca Wasser, and Chris Dougherty, Dangerous Straits: Wargaming a Future Conflict Over Taiwan (Washington, DC: Center for a New American Security, 15 June 2022), 6.
2. Joseph R. Biden and Yoshihide Suga, “U.S.-Japan Joint Leaders’ Statement: ‘U.S.-Japan Global Partnership for a New Era,’” The White House Briefing Room: Statements and Releases, 16 April 2021.
3. Steven Chan and William Safran, “Public Opinion as a Constraint Against War: Democracies’ Responses to Operation Iraqi Freedom,” Foreign Policy Analysis 2, no. 2 (April 2006): 153–55.
4. Jesse Johnson, “In Major Shift, Kishida Sets Defense Spending Target at 2% of GDP for First Time,” The Japan Times, 29 November 2022.
5. Kenneth B. Pyle, “Japan’s Return to Great Power Competition: Abe’s Restoration,” Asia Policy 13, no. 2 (April 2018): 70.
6. Jeffrey W. Hornung, “Revising Japan’s Constitution: Much Ado about Nothing,” Texas National Security Review, 21 March 2018, 4–5.
7. Michael J. Green, Line of Advantage: Japan’s Grand Strategy in the Era of Abe Shinzo (New York: Columbia University Press, 2022), 94–95.
8. Craig Kafura et al., “Strong Partners: Japanese and American Perceptions of the U.S. and the World,” The Chicago Council on Global Affairs, 29 March 2022, 2.
9. Kafura et al., “Strong Partners,” 10.
10. Adam P. Liff and Dalton Lin, “The ‘One China’ Framework at 50 (1972–2022): The Myth of ‘Consensus’ and Its Evolving Policy Significance,” The China Quarterly 252 (26 September 2022): 978–80.
11. Liff and Lin, “The ‘One China’ Framework at 50,” 978.
12. North Atlantic Treaty Organization, “The North Atlantic Treaty” (Washington, DC: North Atlantic Treaty Organization, 1949).
13. Ministry of Foreign Affairs of Japan, “Treaty of Mutual Cooperation and Security Between Japan and the United States of America” (Tokyo: Ministry of Foreign Affairs of Japan, 1960); and Mike M. Mochizuki, “Tokyo’s Taiwan Conundrum: What Can Japan Do to Prevent War?” The Washington Quarterly 45, no. 3 (October 2022): 88.
14. Green, Line of Advantage, 85.
15. Adam P. Liff, “Kishida the Accelerator: Japan’s Defense Evolution After Abe,” The Washington Quarterly 46, no. 1 (Spring 2023): 70.
16. Shaurav Gairola, “DSEI Japan 2023: Japan Expects to Induct Upgraded Type 12 SSM by 2026,” Janes Defence News, 11 September 2023; Takahashi Kosuke, “PM Kishida Announces Japan Will Acquire 400 Tomahawk Missiles From U.S.,” The Diplomat, 28 February 2023; Matthew M. Burke and Keishi Koja, “Japan Inks Deal to Add Submarine-Launched Missiles by Fiscal Year 2027,” Stars and Stripes, 13 April 2023; and Miya Tanaka, “Japan and U.S. Plan Joint Research on Defending Against Hypersonic Weapons,” The Japan Times, 15 September 2022.
17. Liff, “Kishida the Accelerator,” 74.
18. Hu Jintao, Report to the 18th National Congress of the Communist Party of China (Beijing, China: National Congress of the Communist Party of China, 2012), 15; and Xi Jinping, Report to the 19th National Congress of the Communist Party of China (Beijing, China: National Congress of the Communist Party of China, 2017), 27, 48.
19. Green, Line of Advantage, 54.
20. Shinji Yamaguchi, “The Transition in China’s Policy Toward Taiwan,” in NIDS China Security Report 2017: Change in Continuity: The Dynamics of the China-Taiwan Relationship, ed. Tetsuo Murooka et al. (Tokyo: The National Institute for Defense Studies, 2017), 12–17.
21. Ministry of Finance of Japan, “Trade Statistics of Japan: Value by Country”; Japan External Trade Organization, “FDI Stock (Based on International Investment Position, Net)/Inward,” Unpublished Raw Data, JETRO Trade and Statistics, 27 May 2022; and Manpreet Singh, Karen M. Sutter, and John F. Sargent Jr., Semiconductors and the Semiconductor Industry (Washington, DC: Congressional Research Service, 2023), 2–3.
22. Ministry of Finance of Japan, “Trade Statistics of Japan: Value by Country.”
23. Laura Silver, Christine Huang, and Laura Clancy, “How Global Public Opinion Has Shifted in the Xi Era,” Pew Research Center Blog, 28 September 2022.
24. Atsushu Yasutomi, “Combat-Related Death of Soldiers and Public Support for Military Missions Abroad: The Case of Japan,” Comparative Culture, The Journal of Miyazaki International College 23 (2018): 51–53; and Adam P. Liff, “Japan’s Defense Reforms Under Abe: Assessing Institutional and Policy Change,” in The Political Economy of the Abe Government and Abenomics Reform, ed. Takeo Hoshi and Phillip Y. Lipscy (Cambridge, UK: Cambridge University Press, 2021), 493.
25. Sheila A. Smith, Japan Rearmed: The Politics of Military Power (Cambridge, MA: Harvard University Press, 2019), 57–59.
26. Smith, Japan Rearmed, 69–71.
27. The White House, National Security Strategy of the United States (2022) (Washington, DC: The White House, 2022), 22; and Adam P. Liff, “The U.S.-Japan Alliance and Taiwan,” Asia Policy 17, no. 3 (July 2022): 130–32.
28. This comment was made by Prime Minister Abe after he left office. See “Abe Hints at Japan’s Possible Military Role in Taiwan Contingency,” The Japan Times, 14 December 2021.
29. Kyla H. Kitamura and Mark E. Manyin, Indo-Pacific Economic Framework for Prosperity (Washington, DC: Congressional Research Service, 2023).
30. LtCol Brian Kerg and Maj Chris Denzel, USMC, “Get Multinational Warfighting Right, Before It Matters,” U.S. Naval Institute Proceedings 150, no. 5 (May 2024).
31. Ministry of Defense, The Guidelines for Japan-U.S. Defense Cooperation (2015) (Tokyo: Japan Ministry of Defense, 2015), 3–4.
32. Kosuke Takahashi, “Japan Should Send Its Naval Ships through the Taiwan Strait,” Nikkei Asia, 5 July 2022; and Heather Mongilio, “USS Higgins Joins Canadian Warship to Transit Taiwan Strait,” USNI News, 20 September 2022.
33. Ting-Hua Chien and Yi-Chen Hung, “A Review of Defense Development in Japan and Taiwan,” in Defense Policy and Strategic Development: Coordination Between Japan and Taiwan, ed. Fu-Kuo Liu, Dean Karalekas, and Masahiro Matsumura (Hackensack, NJ: World Scientific Publishing, 2022), 311.
34. The White House, National Security Strategy of the United States (2022), 7.
