The title to Formosa was renounced by Japan in the peace treaty, but was not transferred to China. The United States has an inchoate but legitimate interest in Formosa.
Memorandum of Conversation: China Item
Date: October 18, 1954, Washington
Subject: Consultations with the United Kingdom and New Zealand
Reverting to Formosa the Secretary [of State Dulles] stated that the U.S. has an inchoate but legitimate interest in Formosa, title to which was renounced by Japan but was not transferred to China. From an international standpoint it would seem therefore that we are in a better position to defend Formosa than would be the case if Formosa were a part of China.
[ source: United States Department of State / Foreign relations of the United States, 1952-1954. China and Japan (in two parts), (1952-1954), page 775 ]
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[Chinese version] https://www.twdefense.info/trust3/frusch-1954au.htm