In the peace treaty, Japan has merely renounced sovereignty over Taiwan, but there has been no other disposition. The United States also has an interest in Taiwan and could assert a legal claim to the island(s). Hence, the disposition of Taiwan is not merely an internal Chinese problem.
Memorandum: The Department of State
Date: July 1, 1955
Subject: Lessening of Tension in the Taiwan Area
. . . . Even the juridical position of Taiwan is in doubt. The United States also has an interest in Taiwan which we got away from Japan. Japan has merely renounced sovereignty over Taiwan which has not been disposed of by the peace treaty and not ceded to anyone. Consequently the United States could assert a legal claim until Taiwan is disposed of by some means. We cannot, therefore, admit that the disposition of Taiwan is merely an internal [Chinese] problem.
[ source: United States Department of State / Foreign relations of the United States, 1955-1957. China, Volume II (1955-1957), page 619-620 ]
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