According to a report from Japanese news agency Jiji Press, a Chinese diplomatic document from 1950 shows that, at the time, China did not consider the Diaoyutai Islands (釣魚台), known as the Senkaku Islands in Japan, to be Chinese territory.
Japanese politician Yoshihide Suga thinks the document formed the basis for discussions between 63 Chinese diplomats and academics at the time and that it is “a very important find” for Japan. And not only that: The report also mentions that according to the interpretation of Yasuhiro Matsuda, a professor in the Institute for Advanced Studies on Asia at the University of Tokyo, the document proves that Chinese officials in 1950 considered the Diaoyutais to be part of the Ryukyu Islands.
I do not know if such a document really exists, and I have no way of knowing whether it is a forgery.
However, even if it does exist, and even if it is real, such a historical document could have a certain validity and investigative value from an international law perspective. Legally speaking, though, it would have almost no binding effect.
First, documents for internal discussion are only drafts that are rarely made public.
The only purpose of this document was to discuss the handling of the Diaoyutais issue, and it was an internal compilation of opinions within the Chinese government.
It is highly questionable whether a draft document used for internal discussion which was never made public has any binding legal power under international law.
Second, even if Japan were to use this document to demand that China be “estopped” — meaning to be legally barred from alleging or denying something because of one’s own previous actions or words to the contrary — from claiming that the Diaoyutais belong to China, it would not be a very persuasive argument.
Leaving aside the issue of how the International Court of Justice and experts of international law differentiate estoppel from acquiescence, there is relatively little disagreement that successfully demanding that an estoppel be imposed requires that the country making the demand believes the statement of the counterpart to be true, and based on this belief does or does not take some specific action.
If the country making the statement later denies the truth of that statement, then the country that believed the statement to be true must suffer negative consequences or sustain losses from that denial. If that occurs, the country making the statement may not deny its legal responsibilities following from that statement.
However, this document has never been made public, and that raises the question of how Japan, unaware of the document’s existence, would be able to claim that it believed it to be true, or how it would be able to claim that it, as a result, had or had not taken some specific action.
It would thus be preposterous to claim that it had caused Japan to suffer negative consequences or sustained losses.
The fact is that in territorial disputes strongly influenced by nationalism, it does not matter how vulnerable this kind of evidence is to scrutiny or how preposterous it is. What counts is that it is convincing to oneself and that it makes oneself believe that one has sovereignty over that particular piece of land.
It is more likely that the Japanese government is making such a big deal of this because it wants to prove to the Japanese public that the Diaoyutai Islands are part of Japanese territory rather than because it feels that it has revealed important new evidence.