A Chinese military intervention against Taiwan represents a major security threat for Japan. So it is not surprising that a Japanese poll found 74 percent of respondents supportive of their government engaging to advance peace and stability in the Taiwan Strait. Tokyo’s potential role in a military contingency involving Taiwan has also been in the spotlight, however, following increased Chinese and U.S. tensions over the island and a series of comments by senior Japanese officials, including Deputy Prime Minister Taro Aso.
Although Japan’s response in a Taiwan contingency would ultimately reflect the nature of the threat, the U.S. approach, and the broader international reaction, Japan’s constitution and security legislation create legal limits on Tokyo’s ability to defend Taiwan. Yet these limits remain little explored with respect to various Taiwan scenarios, within either Japanese or U.S. policy circles. Because Japan’s security legislation is so complex, particularly after changes that entered into force in 2016 to expand the authorities of the Self-Defense Forces (SDF), a potential Japanese response to a Taiwan contingency is much less clear than it may appear on the surface.
This article briefly outlines the range of Japanese responses to a Chinese invasion or blockade of Taiwan and then examines two sets of key authorities — those related to an “important influence situation” and to a “survival-threatening situation.” The article argues that the authorities under a survival-threatening situation are less likely to be applicable to a defense of Taiwan than recent commentary might suggest. Both the survival-threatening situation and the important influence situation, moreover, present ambiguities and conditionalities that Japanese and U.S. planners should clarify together. Doing so would eliminate potential confusion, ensuring that the U.S.-Japanese alliance can function smoothly in relation to Taiwan and thus strengthening the deterrence that is key for the peace and stability that Japan so strongly desires.
What’s On the Books
Article 9 of Japan’s constitution renounces war and the use or threat of force to settle international disputes. The use of force in self-defense is permitted in response to an armed attack against Japan (we’ll place an asterisk here and come back to it), but only if an armed attack is initiated, not merely if there is a likelihood or threat of attack. If a Chinese attack on Taiwan involved any attack on Japanese territory, from individual islands to U.S. bases, Japan could respond with force in self-defense using a spectrum of military operations. However, Japan’s use of force would be permitted only in the absence of other “appropriate means” and to the “minimum necessary extent.”
Absent a direct attack on Japan, Japanese action can take various forms, depending on the circumstances. Perhaps most pertinently, Japan would have the option to allow the United States to use U.S. bases in Japan for a military response to a Taiwan attack, based on prior consultation requirements relating to “the use of facilities and areas in Japan as bases for military combat operations to be undertaken from Japan.” Historically, Japan has maintained public ambiguity about its willingness to provide acquiescence for such a request in relation to Taiwan.
Japan can also respond to an important influence situation, which comprises contingencies short of armed attack on Japan that, if left unaddressed, could develop to threaten Japan’s peace and security. In such a situation, Japan can provide support for U.S. and other forces responding to the contingency. Japanese support may include search and rescue activities, ship inspections, and logistics support, with the last encompassing such elements as use of facilities, supply chains, transportation, communication, and repair and maintenance.
Additionally, there is one scenario short of a direct armed attack against Japan where the country is permitted to use force in self-defense, per the asterisk we placed earlier. This involves the survival-threatening situation, which refers to “a situation where 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.” In such a scenario, Japan could undertake similar military operations to those designed to respond to an attack against Japan, including in collaboration with the United States or other countries. This is effectively collective self-defense, but it is a narrower species of collective self-defense than traditional interpretations because Japan can only come to the defense of another nation if its own survival is directly jeopardized and not simply because that nation happens to be an ally or friend.
Both the important influence situation and survival-threatening situation designations are part of a controversial package of security legislation, passed in 2015 to attendant public protests and sharp divisions within the Diet, that entered into force in 2016. Opponents of the legislation feared it could be used to drag Japan into U.S. military adventurism. The administration of then-Prime Minister Shinzo Abe, meanwhile, argued that it was necessary to address changing regional and global security environments and had built-in limitations.
Realistically, the Japanese government — like any government — will try to do whatever it believes is necessary for the country’s security and build the requisite argument to back that. However, such an argument will need to pass muster with the Diet, which is required to approve military operations under the security legislation. As a result, the government will need to provide a solid legal basis and clearly identify why the specific proposed response is needed, especially if it involves a Japanese use of force. This is important given the presence of parties in the Diet with restrictive views on the use of force and collective self-defense, including the ruling party’s main coalition partner.
When an Attack on Taiwan Threatens Japan’s Survival
The applicability of the survival-threatening situation designation for a defense of Taiwan is thus interesting to examine, particularly given Aso’s direct reference to the term when he noted 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.” One significant point that remains unknown is whether Taiwan qualifies as a foreign country for the purposes of Japan’s relevant security laws, since Japan does not officially recognize Taiwan as a separate county from China, despite its relations with Taipei. How much this technicality might matter in an actual crisis likely depends on the mood in the Diet, but in Japan’s rule-conscious political culture, the question might present a legal conundrum. Leaving the issue of Taiwan’s status as a foreign country aside, the intentions behind the designation are also worth examining.
Although the specifics of when an attack on a foreign country might directly threaten Japan’s survival are not defined in relevant laws, it is telling that all the examples of the potential application of the designation provided by the Abe government and a legal advisory panel convened to examine the issue involve the United States. Because Japan’s security is so deeply linked to the protective potential of the United States, it is not difficult to see how an attack on the United States that might decrease U.S. defensive or offensive capacity could jeopardize Japan’s defenses and thereby threaten its survival. An attack on Taiwan would not impact the mechanics of Japan’s security provision in such a way.
Indeed, an attack on the United States in a Taiwan contingency may be more likely to spur a survival-threatening situation designation than an attack on Taiwan itself. For example, U.S. ships under missile attack by Chinese forces could request Japanese assistance — a scenario similar to one the advisory panel contemplated (in the general case) in its justification of the need for collective self-defense permissions. Abe himself warned that a failure to protect U.S. ships when requested could unravel the very fabric of the U.S.-Japanese security alliance upon which the country’s security rests. The likelihood of such an outcome would obviously depend on the nature and severity of the specific case, but the example underscores the U.S.-centric focus the Abe administration seemingly intended for designating a survival-threatening situation.
Regardless of the original intent, the language describing a survival-threatening situation is flexible enough to apply directly to Taiwan if the Japanese cabinet determined such a course to be necessary. As noted, however, a solid case would be needed to secure Diet approval for military operations under the law. According to guidance suggested by the advisory panel, the clearest case could be made if there were a high probability that an attack on Taiwan would lead to a direct attack against Japan. Although such a scenario may appear open-ended, only a few specific cases would likely qualify without ambiguity. Examples help illustrate the point.
Take an attempted Chinese invasion of Taiwan. This action alone would send extremely worrying signals to Tokyo about Beijing’s intent and self-restraint, and, if successful, could facilitate a Chinese attack on Japanese territory or supply chains. Such a scenario would doubtless put the Self-Defense Forces on high alert. However, absent a causal and temporal link between the attack on Taiwan and an attack on Japan — such as clear indications that China intended to attack Japan from Taiwanese territory once it gained control — it would be difficult to argue that a Japanese use of force in defense of Taiwan was necessary to protect Japan from attack. Even use of force for the defense of Japan itself, as noted earlier, would only be allowed if China initiated an attack on Japan, not merely because it might now be in a better position to initiate one.
Imagine, instead, if there were clear information or intelligence that China planned to use the invasion of Taiwan as a necessary part of a sequenced attack on Taiwan and Japan — one focused, perhaps, on the Chinese-claimed and Japanese-administered Senkaku Islands, or even on other islands in Japan’s Okinawa prefecture. In such a scenario, an attack on Taiwan could constitute, in effect, the initiation of an attack on Japan, closely connecting an armed attack against Taiwan with a direct threat to Japan’s survival. The defense of Taiwan could thus be seen as integral to the defense of Japan. Although variations on the situation might also qualify, this is the basic scenario under which a Chinese invasion of Taiwan would likely present a survival-threatening situation for Japan.
If China were to opt to blockade Taiwan, it might also be possible to apply the survival-threatening situation designation, but again, likely only in a very narrow range of circumstances. First, Japan would need to consider the blockade to constitute an armed attack — for example, in the gravity of its scale and effects on Taiwan. Second, per the guidance of the advisory panel, the blockade would need to critically impact Japan or its citizens, perhaps by strongly harming Japan’s economy. For Japan to need to use force to defend Taiwan due to such effects, however, the blockade would need to critically impact Japan through its impact on Taiwan specifically. Since Taiwan is Japan’s fourth-largest export marketand eighth-largest import territory of origin, this could be plausible if a blockade were to go on long enough. Again, there could be variations to this scenario, but very few exist that would meet the pass-through criterion.
All in all, the potential cases under which an attack on Taiwan would threaten Japan’s survival in accordance with relevant security laws appear very limited. There is one caveat here worth exploring. The advisory panel also suggested that a case might be a made for a survival-threatening situation if the “international order itself could be significantly affected” as the result of an attack on a foreign country. This notion could introduce some flexibility for Japanese decision-makers. China’s successful reunification with Taiwan by force would certainly affect the regional order and, in turn, U.S. power in the region. There may be debate within Japan about whether such a scenario would significantly impact the international order itself, however.
Ultimately, Tokyo is unlikely to authorize use of force in defense of Taiwan unless it feels it absolutely must, because this will bring it into direct conflict with China. However, the lack of specificity still leaves a range of scenarios for U.S. military planners to consider and/or eliminate, even leaving aside the question of the international order. Moreover, an understanding of both Japanese law and Japanese interpretations of international law is required, making this a complex task.
When an Attack on Taiwan Could Develop to Threaten Japan’s Security
If a contingency involving Taiwan did not rise to the level of a survival-threatening situation, it would nonetheless present serious concerns and risks for Japan. This is where the important influence situation designation comes in. The examples of a potential important influence situation provided by the Abe government and the advisory panel are again telling and boil down to U.S. forces responding to an attack by one regional country against another. One example involves “a situation where an armed attack against another country occurs in Japan’s neighboring area and the United States is exercising the right of collective self-defense in support of said country,” and “if such a situation is left untouched, the conflict would enlarge, and eventually, Japan itself would be affected by the conflict.” This example presents circumstances very similar to a potential Chinese invasion of Taiwan.
Although all the available examples of an important influence situation involve an actual armed attack on a third country, the occurrence of an armed attack is not an explicit requirement to define such a situation, so it is likely that a blockade of Taiwan would qualify, even one not devastating enough to constitute an armed attack. This is useful when considering that a quasi-blockade or “quarantine” limited to military materiel may be a more effective strategy for China than a full blockade, according to a special report from the Council on Foreign Relations. It is certainly plausible that a blockade or quarantine of Taiwan would fit the criteria for a situation that, if left unaddressed, could develop to threaten Japan’s security.
The pertinent aspect of an important influence situation with respect to Japanese support activities, however, is that it requires a U.S. response to support. The nature and circumstances of that response would likely be determinative. This is particularly relevant because Japanese and U.S. interpretations of collective self-defense and the legal use of force differ. It is unlikely that Japan would be able to provide support activities for a U.S. response that it did not see as consistent with international law. Take, for example, a Chinese quarantine of Taiwan. If the United States were to respond to the quarantine by dispatching warships to the area to monitor the situation, Japan could likely refuel or supply these ships or provide other relevant support activities.
In contrast, imagine a quarantine case in which the United States decided to respond with force. If Japan did not categorize the quarantine as serious enough to constitute an armed attack, Tokyo might not consider a U.S. use of force in defense of Taiwan as a legitimate example of collective self-defense under the United Nations Charter, constraining its ability to act. It is, of course, unclear that the United States itself would respond with force in such a scenario, but the case is meant to illustrate conditionalities at play in Japanese support authorities. It also shows that the important influence situation designation is not wholly free from the issue of Taiwan’s status as a foreign country, even though the language in the law does not reference the term. Here, Taiwan’s status would certainly play into the perceived legality of a U.S. use of force under international law.
Ultimately, an important influence situation designation is more flexible than a survival-threatening situation designation, and thus more likely to apply to a Taiwan contingency. However, the relevant variable for an important influence situation is the nature not only of the threat itself, but also of the U.S. response. In this regard, the more information Japan has about U.S. intentions and options, the better clarity it can generate about its own possible responses.
Providing Needed Clarity
The ambiguities and conditionalities surrounding the applicability of the survival-threatening situation and important influence situation designations to Taiwan point to the need for U.S. and Japanese officials to think through the many potential scenarios in a Taiwan contingency and clarify to each other, privately, their potential responses. This would not require either partner to commit itself to any specific course of action. It would simply clarify which response options are actually on the table and how such options may be both shaped and constrained. According to government sources, Japan is already conducting an internal review of its options for a Taiwan contingency, a necessary first step for such consultation.
If it is not already doing so, Japan should also seek internal legal clarity on whether and under what circumstances Taiwan could count as a foreign country for the purposes of Japanese security law. Sharing this information privately with the United States and seeking U.S. views on the same would be a useful follow-up action. Understandably, Japan may want to condition its views on Taiwan’s status based on how other members of the international community proceed. Such nuances could be included in Japanese information sharing with the United States.
Additionally, a Taiwan contingency is likely to require quick thinking and decision-making. This will be important not only for U.S.-Japanese coordination, but also for Japan domestically. Most of the authorities granted to the Self-Defense Forces in 2016 remain unutilized and the internal coordination processes required legally for their deployment untested. To this end, it may be useful for Japanese authorities to translate the results of their own Taiwan review and any subsequent consultations with the United States into an internal exercise to ensure that national and local officials are able to act quickly and seamlessly. Relatedly, the Japanese government should work to increase the understanding of Diet members regarding various potential Taiwan scenarios, given the Diet’s approval role.
Some might argue that the lack of clarity surrounding Japan’s designations of survival-threatening situations and important influence situations is helpful as a form of deterrence. If the issue were simply about Japan’s intentions, as in the case of permission regarding U.S. use of bases for a military defense of Taiwan, such an argument might hold water. However, in the case of Japan’s legal authorities for addressing a Taiwan contingency, the key question relates to Japan’s options rather than its intentions. By creating a space for confusion by U.S. military planners and Japan’s own decision-makers, the ambiguities and conditionalities related to the application of these designations to Taiwan undermine deterrence and give China an advantage that these allies need not concede. Remedying this confusion will help strengthen deterrence and ensure that a Taiwan contingency remains purely hypothetical.