The South Korea-Japan talks that lasted for 13 years and eight months were in effect a process among South Korea, Japan and the U.S. carried on under the influence of the U.S.
During the Korean War, the U.S. urged South Korea and Japan to forge diplomatic ties in order to enhance the solidarity between anti-communist nations. Afterwards, the U.S. made efforts to bring the two countries together, whenever South Korea and Japan argued over the amount of South Koreas claim for compensation to Japan and its legitimacy.
In 1945, Japanese property in Korea was reverted to South Korea under Directive 33 from the U.S. Army Military Government in Korea, and as Japan claimed its ownership of the reverted property, the South Korea-Japan talks came to a deadlock. In response, the U.S. sent the two countries a memorandum that re-interpreted the fourth article of the San Francisco Peace Treaty, which validated Directive 33. In its State Department memorandum in December 31, 1957, the U.S. sided with South Korea by saying, Japan cannot claim back its property in Korea. As a result, Japan withdrew its demand.
On October 20, 1962, then Korea Central Intelligence Agency Director Kim Jong-pil met with then Japanese Foreign Minister Masayoshi Ohira to negotiate the size of compensation but failed to reach an agreement. On November 12, they had another meeting, agreed on the compensation and wrote the landmark Kim-Ohira Memorandum.
On November 4, in between two meetings above, the Korean mission to Japan sent an official letter to the Foreign Ministry that said Director Kim Jong-pil visited the U.S. and met Secretary of State Dean Rusk. The meeting gave a hint from which one can infer that State Secretary Rusk found out the minimum and maximum amounts of compensation of South Korea and Japan, and then proposed the $300 million plus compromise to encourage a final deal.
On February 28, 1964, the Korean Ambassador to the U.S. reported back to his home country in writing. According to the document, Secretary Rusk remarked, The normalization of diplomatic relations will be of help to the South Korean economy I hope that they wrap up the talks before the session of Japans Diet ends in mid-May.
On July 10 of the same year, then U.S. Ambassador to Japan Edwin Reischauer expressed his opinion, saying, If it is hard to reach an early agreement; the establishment of a Japanese mission to South Korea may be allowed to practically revive diplomatic relations.
In April 29, 1965, Assistant Secretary of State for Far Eastern Affairs William Bundy met the Korean Ambassador to the U.S. In the meeting, the assistant secretary said, The U.S. strongly hopes to see an agreement before the visit by President (Park) to America Without an event as historical as a South Korea-Japan agreement, it would be difficult to persuade members of Congress (to grant economic assistance to South Korea).
When Assistant Secretary Bundy came to South Korea in 1964 before the meeting in April 1965, then Presidential Advisor for State Affairs Yang Dal-seung even drew up a report that argued for setting up a Korean lobbying group in the U.S. (over the South Korea-Japan talks).
Professor Lee Won-deok at Kookmin University, an analyzer of the documents on the talks, noted, If you dig into the vast body of U.S. documents related to the South Korea-Japan talks, you will find out how far-reaching Americas influence was on the talks.