Until the nineteenth century, the term "Sea of Korea" had been used widely in Western maps.
For example, a Portuguese Manuel Goding-You made a map of Asia in 1615, and illustrated the sea between the Korean Peninsula and Japan as "Mar Coria," meaning "Sea of Korea."
Furthermore, in a map created by Robert Dudley in 1646, the term "MARE DI CORAI" (Sea of Korea) is written.
In addition, John Senex, a well-known cartographer of the UK, created a map of Asia in 1710. The map describes the so-called "Sea of Japan" as "The Eastern or Corea Sea."
Also, Herman Mall, a German, wrote the term "Sea of Corea" in his map called "The Empire of China and the Island Nation Japan," which was made in the 1720s.
More maps described the sea on the west side of the Korean Peninsula as the "Sea of Korea" or similar expressions, like the map of Japan by Didier Robert de Bogondi, and a map named "The Empire of Japan divided into seven principal parts and subdivided into sixty-six kingdoms" that was created in the UK.
Even several maps that were made in Japan, including a world map created in 1810 and the map "National Tax Chart of Japan" created in 1866, illustrated the sea as the "Sea of Joseon".
It was when Japan and its imperialism became strong enough to conquer other countries like Korea that the term "Sea of Japan" started to spread.
So, correcting the term "Sea of Japan" is not also a matter of not confusing the public but also cleaning up the vestiges of Japanese imperialism.