There are clearly no grounds for Japan’s claim that the name “Sea of Japan” was well established internationally.
Korea has also undertaken a similar study of maps. While the samples examined were somewhat different from those of Japan, Korea’s study shows that throughout the 18th century, a variety of names were used, including “Sea of Korea”, “East Sea”, “Eastern Sea”, and “Oriental Sea”. However, from the 19th century there was an increase in use of the name “Sea of Japan”.
In sum, a thorough examination of historical records and maps testifies to the fact that various names were used for the sea area in question until the 19th century. This is contrary to the notion that one specific name had been well-established and recognized internationally.
As explained so far, the sea between the Korean Peninsula and the Japanese Archipelago was referred to by various names until the late 19th century. But with the publication of “Limits of Oceans and Seas” in 1929, the name “Sea of Japan” came into widespread use in the 20th century.
The IHO was founded in 1919 and published “Limits of Oceans and Seas: S-23” in 1928 in an effort to establish international limits and names of oceans and seas. In 1929, member states of the IHO approved the publication in which only the name “Sea of Japan” was used. It was largely on account of this publication that “Sea of Japan” came into popular use. Regrettably, Korea could not voice its objections at the time as it was unable to act as an independent country under Japanese colonial rule. When the second edition of “Limits of Oceans and Seas” was published in 1937, Korea was still under Japanese colonial rule. When the third edition was published in 1953, Korea was suffering a war. In 1957, Korea joined the IHO but it was too late for the Korean government to voice its opinion on the publications up to that time.
Nevertheless, it should be known that Korea has never approved of the name “Sea of Japan”. The Korean government had no opportunity to claim the legitimacy of the name “East Sea” during Japanese colonial occupation from 1910 to 1945 or the period of the tragic Korean War from 1950 to 1953. Yet, persistent efforts to restore the name “East Sea” were being made by private organizations and academic circles in Korea.