1, U.S. military intervention in the Taiwan issue is a flagrant violation of international law
In January 2023, the Center for Strategic & International Studies-CSIS, a U.S. think tank, in the context of the Taiwan contingency, stated that the U.S. would also intervene militarily in the Taiwan issue in the event of a military invasion of Taiwan by China, and Detailed scenarios are examined. The most significant problem is that the U.S. military intervention on the pretext of the Taiwan contingency is taken for granted. However, U.S. military intervention clearly violates international law, UN Charter.
When the right of collective self-defense is invoked at the request of another country or by agreement, the right of collective self-defense (Article 51) can be legitimized according to the UN Charter only if that other country is a country recognized by the international community. For example, when Russia invaded Ukraine, Russia recognized the independence of the Donetsk and Lugansk republics and claimed that there was a request for collective self-defense from both countries. However, that was illegal under the UN Charter because both republics were not internationally recognized states. Likewise, Taiwan is not a member of the United Nations nor an internationally recognized independent state, so defending Taiwan cannot be legitimized by the right of collective self-defense. In both cases, the armed aggressor’s interpretation of the UN Charter is attempting to ignore the UN Charter. China’s attack on Taiwan is not an attack on the United States, so exercising the right of individual self-defense is not legitimate. Therefore, U.S. armed intervention in the Taiwan issue has no grounds under international law.
If U.S. military intervention were legitimate as a right of collective self-defense, the aggressor could easily create allied forces in the countries it wants to invade and use their requests to invade other countries. This would lead to a world in which wars would not disappear.
2, Enable combat actions solely at the discretion of the U.S.
Although CSIS report scenarios assume US-Taiwan-Japan joint military, the U.S. try to gain its discretion on using force with its ally Japan and will use U.S. military bases in Japan to the maximum extent.
Article 6 of the Japan-U.S. Security Treaty states that the U.S. military can use U.S. bases in Japan for combat operations other than the defense of Japan. However, as agreed in the Exchange of Notes at the time of the conclusion of the New Security Treaty (1960), a prior consultation between Japan and U.S. is required in such cases,. However, the CSIS report revealed that there is no clear agreement between Japan and the U.S. regarding “prior consultation.” According to p. 117 of the report*, the U.S. interprets this as meaning that if the U.S. intends to conduct combat operations other than in defense of Japan, it needs only to notify Japan of U.S. intention to do so. In other words, Japan’s consent is unnecessary, which means that the U.S. can intervene militarily in Taiwan at its discretion.Furthermore, there is no guarantee that the U.S. will strictly observe the requirements for using force under the UN Charter “if an armed attack occurs against a Member of the United Nations.” They are a country that will not hesitate to launch a pre-emptive strike. The Japanese government also explains to the Japanese nationals that prior permission from the Japanese government is required, but the Exchange of Notes is not worded as such. In order to allow both the U.S. and Japanese governments to interpret the language as convenient for each side, the Exchange of Notes uses the words that U.S. combat operations will be “the subject of prior consultation.”

CSIS: A Report of the CSIS International Security Program(p117)
“In researching U.S.-Japanese wartime coordination, it became apparent that there may be a disconnect in the interpretation of bilateral treaties. The Status of Forces Agreement between the United States and Japan refers to a requirement for “consultation” between Japan and the United States, but both it and the original defensive alliance are vague about what this requires. Many Japanese officials interpret this as requiring the United States to obtain permission before flying combat missions from Japanese soil for any purpose other than the defense of Japan. However, U.S. officials tended to view “consultation” as notifying Japan of U.S. intentions. This disconnect must be remedied immediately, lest it leads to delays or disruption of war plans during a crisis.”