With Beijing’s hostile rhetoric trumpeted and its saber increasingly rattled, Taiwanese are naturally looking to Japan to supplement and complement US military power. The sense of necessity is considerable since the US has experienced serious relative decline vis-a-vis China, now compounded severely by the protracted war in Ukraine and the Gaza conflict.
The US might not be able to cope with three concurrent major regional conflicts in Europe, the Middle East and Northeast Asia, and thus is an increasingly less reliable sole security guarantor for Taiwan.
No wonder Taiwanese felt relieved to learn of former Japanese prime minister Shinzo Abe’s statement in December 2021 at an online forum of the Institute for National Policy Research in Taipei: “A Taiwan contingency is a Japan contingency.” This sounds as if the Japan Self-Defense Forces would intervene in the event of a Chinese invasion of the main island of Taiwan.
Abe’s remark seemed a natural progression from the joint statement that came out of the Japan-US joint summit the preceding April between then-Japanese prime minister Yoshihide Suga, who was Japanese chief cabinet secretary under Abe’s premiership, and US President Joe Biden, saying they “underscore the importance of peace and stability across the Taiwan Strait and encourage the peaceful resolution of cross-Strait issues.”
In August, Liberal Democratic Party (LDP) Vice President Taro Aso, a former Japanese prime minister, delivered a speech at the Ketagalan Forum in Taipei emphasizing the importance of “Japan’s will to fight” alongside the US and Taiwan to deter China from waging a regional war centered on Taiwan.
This reinforces the impression that the LDP government is committed to armed intervention in a possible Taiwan contingency.
In polls by the Taiwan Public Opinion Foundation, Taiwanese have consistently said they expect the Japanese “military” to intervene in the event of a Taiwan contingency and see it only slightly less plausible than US military intervention. Immediately after the outbreak of Russian aggression against Ukraine, their expectations regarding Japanese and US intervention reversed.
However, given Japan’s constitutional and other legal constraints, and its established policy of “exclusively defensive defense,” Taiwanese’s expectation is totally unwarranted.
Under its postwar constitution, Japan “renounce[s] war as a sovereign right of the nation and the threat or use of force as means of settling international disputes,” and does not recognize the “right of belligerency of the state.”
China’s aggression against Taiwan would never constitute an armed attack on Japan and thus would never justify Japan’s “military” fighting against Chinese forces. Japan also lacks any international legal grounds for such military action, because Tokyo abandoned the title of Taiwan’s suzerain by concluding the San Francisco Peace Treaty of 1952 without reassigning it to any party. This means that Japan’s armed forces could never openly fight for Taiwan.
Certainly, the Abe administration in 2015 reinterpreted the constitution in a way that enabled limited exercise of the right of collective self-defense. This is deeply entrenched in the Three Strategy Documents from December last year that are seen as highly active and unambiguous in exerting deterrence against China.
The following three conditions for use of force were set: when an armed attack against Japan has occurred, or when an armed attack against a foreign country that is in a close relationship with Japan occurs and as a result threatens Japan’s survival and poses a clear danger to fundamentally overturn people’s right to life, liberty and pursuit of happiness; when there is no appropriate means available to repel the attack and ensure Japan’s survival and protect its people; and use of force is limited to the minimum extent necessary.
This applies to the defense of US bases, facilities and forces in Japan and US forces on combat missions in the operational theater of the Far East, including Taiwan, given the US is its sole treaty-based ally.
A full-scale Taiwan contingency would most likely involve China attacking the US air base in Kadena on the main island of Okinawa and the Senkaku Islands, known as the Diaoyutai Islands (釣魚台群島) in Taiwan. The Self-Defense Forces would take maximum defensive action against such attacks, which would indirectly, but significantly contribute to the defense of Taiwan. This excludes the possibility that the Self-Defense Forces become involved in a limited Taiwan contingency that occurs primarily over the Taiwan Strait and the main island of Taiwan.
Conversely, Japan’s unilateral intervention basically cannot be authorized and is operationally infeasible due to the dearth of Japan’s power projection capabilities, which would only be available after the completion of a 10-year arms buildup plan that has been agreed to, but essentially still exists only on paper.
Hence, Japan’s armed intervention is plausible in a full Taiwan contingency only through the Japan-US alliance. There would be no unilateral intervention at all.
The political rhetoric of major Japanese political leaders, especially Abe’s, has been heavily constrained by the prevailing domestic policy discourse, which has misled the Taiwanese public and authorities.
It is necessary for Taiwan to recalibrate its expectations of Japan’s intervention and concentrate on reinforcing its own defense capabilities, while enhancing informal defense policy coordination between Taipei and Tokyo.
Masahiro Matsumura is a professor of international politics and national security at Momoyama Gakuin Daigaku, also known as Saint Andrew’s University, in Osaka, Japan.
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