Why Japan Would Violate International Law If It Militarily Intervened to Defend Taiwan (But Why Japan Should Do So Anyway)

by Julian Ku

I’ve been swamped with various projects and distractions here in Taiwan (mostly food-related), so I didn’t notice until today this very interesting Zachary Keck post about how Japan’s recent decision to re-interpret its constitutional provision to allow expanded overseas military activities would enable Japan to help defend Taiwan against an attack from China.  It’s a fascinating post, but it also made me think of an interesting wrinkle that cuts against his argument.  It is almost certainly true that international law prohibits any military action by Japan (or the US) to defend Taiwan from a Chinese attack.

In his post, Keck notes that Japan’s decision to reinterpret its constitution does NOT allow Japan to fully exercise its rights to collective self-defense under international law, but it does allow Japan to provide military support to allies where Japan itself is threatened.  But he then argues that even under this more narrow “collective self-defense” right, Japan could  (and probably would) intervene to assist Taiwan in a military defense against a Chinese invasion.

I think this could be right as a matter of Japanese constitutional law if an invasion of Taiwan could be plausibly construed as a threat to Japan, but there is a strange international law flaw to this argument.  Under black-letter international law, Japan cannot use military force in Taiwan absent China’s consent, even if the Taiwan government requests its assistance.  Why? Because the UN Charter’s Article 51 only authorizes an act of “collective self-defense if an armed attack occurs against a Member of the United Nations.” Taiwan is not a member of the United Nations, and to make matters worse from Taiwan’s perspective, Japan recognizes the government in Beijing as the rightful government of China, and Japan further recognizes that Taiwan is part of China. 

So unless Japan is able to plausibly claim that an attack on Taiwan triggers Japan’s own inherent self-defense right (and I think this is a non-starter as a legal argument), and unless a Chinese invasion could be said to justify humanitarian intervention (another very difficult argument), Japan would violate the U.N. Charter if it used military force in a way that violated the territorial integrity of another UN member (China).  Japan could not invoke its collective self-defense rights unless it recognized Taiwan as an independent nation.  And even that would probably not be enough to satisfy international law requirements, since Japan’s unilateral recognition of Taiwan as an independent state would necessarily satisfy international law either.  And good luck, Taiwan, getting U.N. membership.

By the way, this analysis applies equally (or even with greater force) to the United States.  The U.S. quasi-defense guarantee to Taiwan has it completely backwards (from a legal point of view):

  • If Taiwan declares independence, the U.S. has signaled it would not consider itself bound to defend Taiwan against a Chinese invasion. Yet that would be (at least in theory) one state (China) committing aggression against another state (Taiwan), and almost certainly illegal.
  • If Taiwan keeps the status quo and does not declare independence, and China still invades, the U.S. has signaled that it would come to Taiwan’s defense. But that would be one state (China) using force within its own territory to put down secessionists (a la Ukraine) and almost certainly legal.

So the U.S (and maybe Japan) are now committed to defend Taiwan only in a situation that would require the US and Japan to violate the U.N. Charter.  It’s international-law-bizarro world!

Of course, this bizarro-from-a-legal-point-of-view policy suits U.S. purposes, since it is the policy most likely to avoid military conflict with China.  But it also reveals how use of force rules in the U.N. Charter have little relevance to shaping the behavior of the U.S., Japan (and probably China) in any conflict over Taiwan.  Japan and the US should (and probably are) ready to ignore these legal rules when making their determinations about whether to defend Taiwan.  And all in all, that’s a good thing (especially while I am still here in Taipei!).


13 Responses

  1. I always thought that the reference to member states in article 51 is without prejudice to the right of collective self-defence applicable also to non-member states. This right comes from customary law, and therefore extends beyond the UN Charter, as long as it is not in direct contradiction with it. And here there would not be direct contradiction – article 51 would simply not apply, since it does not say that the right of collective self-defence is limited to UN member states. It seems to me that the opposite reading would have prevented the US from helping West Germany in the face of Soviet attacks before W. Germany joined the UN, which is of course strange.

    And on the statehood of Taiwan, since recognition is merely declaratory, it does not matter what Japan says officially: Taiwan is clearly a separate subject of international law from China. The opposite view would lead to the impossible result that, were Taiwan to bomb (for some strange reason), say, Seoul, then Korea could counterattack against Beijing, and Beijing would not object (for fear of showing that Taiwan is not part of China). This scenario – and the most likely international response to it – instead shows that Taiwan is indeed an independent subject of international law, or else its actions would be attributed to China – which they never are.

    If this is true, then Taiwan must be able to exercise self-defence, and able to be the object of collective self-defence by any other state. Japan might be violating its constitution, but on this reading it might not be violating international law.

  2. Guy has a very good point — customary international law would allow a state like Japan or the United States to engage in collective self-defense. And then there would be the issue regarding Article 2(4).
    I view Article 2(4) as merely proscribing three types of uses of force. Assuming that Taiwan is an independent state (according to a few states it is) or nation [recall that there are other actors than the state that have formal participatory roles in the international legal process], a use of force on Taiwan to defend Taiwan would not be “against” the territorial integrity of China or “against” its political independence, and it would arguably be in a manner that is generally serving of the various principles of the Charter in the long run.

  3. p.s. I have not checked elsewhere, but Julian, are you sure that Japan has recognized China’s sovereignty over Taiwan as such? Of course, the PRC exercises absolutely no control over any part of Taiwan. Further, in terms of self-determination of peoples, I recall that the majority of Taiwanese (especially younger persons) identify themselves as Taiwanese and not Chinese.

  4. Response…Assuming that Taiwan is an independent state (according to a few states it is) or nation [recall that there are other actors than the state that have formal participatory roles in the international legal process]

    Putting diplomatic neutrality and niceties aside, we are talking about the on-going effects of recognition of belligerency in the past and the consequences for the territorial and political entities that emerged from a Chinese civil war.

    The WTO and its member states formally recognized Taiwan as a separate customs territory in 2002.

    22 U.S. Code § 3301 repeatedly refers to “the people on Taiwan” as an entity with the requisite international personality to exercise self-determination, e.g. they are a people entitled to weapons of self-defense to maintain their territorial integrity. The US “considers any effort to determine the future of Taiwan by other than peaceful means, including by boycotts or embargoes, a threat to the peace and security of the Western Pacific area and of grave concern to the United States.” It is definitely NOT treated as a matter falling solely within the domestic jurisdiction of the government of China.

  5. The status of Taiwan is always such a complex issue to discuss. However, I keep wondering: when we talk about Taiwan, are we talking about the Republic of China (ROC) or the KMT/former DPP government of the ROC?
    If it is the former case, then take a look at the ROC constitution, art. 4, “The territory of the Republic of China according to its existing national boundaries shall not be altered except by resolution of the National Assembly.”
    The ROC Constitution was adopted on December 25, 1946, by the National Assembly convened in Nanking, and so far no alternation concerning the territory has been made. In this regard, the essentially legal issue between Beijing and Taibei is actually which government has the legitimacy for China. It would appear so theoretical that may be no one in reality would believe it. Yet still, it is true.

  6. Again, I think the principle of effectiveness should rule: Beijing does not have control over Taiwan; Taiwan does not have control over mainland China. The two act like States for all intent and purposes; the acts carried out by one of them are never attributed to the other; any conflict between them would likely be governed by the law of international armed conflict (or at least the IOCRC would insist that this be the case).
    What each one of them says in their internal documents for political purposes is largely irrelevant, in my view, for international law purposes.

  7. What, in all these words, justifies Chinese invasion of Taiwan? What is the point of the UN in all this?

  8. This writer has been and will always be biased in favour of PRC a country who disregards the law of the sea with its then-nine-and-now-ten-dash line using its HYSY-98n as mobile national territories and strategic weapons to progressively wrest control of offshore neighbouring areas.

    In other words, he has been and will always be a China’s spin Dr.

  9. Japan follows international law and the postwar treaty systems and does not recognize Chinese sovereignty over Taiwan. In fact no internationally-recognized document gives China sovereignty over Taiwan in either its ROC or PRC incarnation. Hence Ku has erred doubly; his conclusion is forced by his poor understanding of the status of Taiwan. China would be grossly violating the UN charter in an attack on the unincorporated territory of Taiwan, whose status awaits determination and whose population should, under law and practice, be given a referendum on their status.


  10. “‘The ROC Constitution was adopted on December 25, 1946, by the National Assembly convened in Nanking, and so far no alternation concerning the territory has been made. “”

    That is incorrect, since the 9-dash line, first promulgated by the ROC, postdates this constitution.


  11. Response…to the query about whether Japan has recognized the PRC’s sovereignty over Taiwan: no, it has not. In the 1972 normalization agreement, China stated that Taiwan was an integral part of the PRC and Japan took note of this position. From a legal standpoint, Japan considers the status of Taiwan to be “unresolved” and has said so several times. Jiang Zemin’s effort to get this changed as part of his 1998 visit there backfired badly.

  12. @Julian Ku: Where on earth did you get your sources?

    Quoting you:”Japan recognizes the government in Beijing as the rightful government of China, and Japan further recognizes that Taiwan is part of China.”

    The Chinese version might say so, but the Japanese version says different. The Japanese version of the Joint Communique of the Government of Japan and the Government of the People’s Republic of China signed on September 29, 1972 says:

    “The Government of Japan recognized the Government of the People’s Republic of China as the sole legal government of China. . . .
    The government of Japan FULLY UNDERSTANDS AND RESPECTS THE STAND OF THE PEOPPLE’S REPUBLIC OF CHINA that Taiwan is an inalienable part of the territory of the People’s Republic of China and it firmly maintained its stand that Taiwan was not its territory.

    Between “understand and respect the Chinese stand (the preposterous, legally unattainable Chinese claim) to acknowledging that Taiwan is Chinese territory, there’s a gap I would think twice before jumping.

    But you, Julian jumped. How reckless. Might be genetical. Check your ancestry. I am channeling a Japan-sympathizer who fell victim of KMT thugs when he was branded a “hanjian” in 1937 Shanghai.

    Contemporary Chinese history is so. . . elusive?

    As for your scholarship . . . Another blotch on Yales’ escutcheon, I am sorry to conclude….

  13. I think you need to read this response to your article and reconsider your misinterpretation of international law and the UN Charter.


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