The Kinmen and Mazu island groups have continuously been Chinese territory, unlike Formosa and the Pescadores. Under the Japanese peace treaty, Formosa and Pescadores have an inchoate juridical status.
Telegram: The Secretary of State to the Dept. of State
Date: September 27, 1954
Subject: Discussions with British Foreign Secretary
. . . . these [Kinmen and Mazu] offshore islands have continuously been Chinese territory in distinction to Formosa and Pescadores which have inchoate juridical status under Japanese peace treaty.
[ source: United States Department of State / Foreign relations of the United States, 1952-1954. China and Japan Volume XIV, Part 1 (1952-1954), page 663 ]
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