Takeshima was treated as part of Japanese territory under the San Francisco Peace Treaty
Signed in September 1951, the San Francisco Peace Treaty states that Japan recognizes the independence of Korea and renounces “Korea, including the islands of Quelpart, Port Hamilton and Dagelet.” The treaty thus excludes Takeshima from the areas to be renounced by Japan.
Prior to the signing of the treaty, in July 1951, a request made by the ROK to include Takeshima to the areas to be renounced by Japan under the peace treaty was explicitly rejected by the United States. The government of the United States responded to the Korean government through the letter from the then US Assistant Secretary of State for Far Eastern Affairs, Dean Rusk, stating that the rejection was on the grounds that Takeshima had never been treated as Korean territory and that Korea had at no point claimed sovereignty over Takeshima in the past. This fact unequivocally shows that Takeshima is an inherent part of the territory of Japan.
[Letter from the then United States' Assistant Secretary of State for Eastern Affairs, Dean Rusk (excerpt)] (Photo: Ministry of Foreign Affairs)