The term 'East Sea' has been used for more than two thousand years and numerous historical records including old maps provide evidence for this. The term appears in the 'King Dongmyeong' chapter of Samguksagi, the oldest existing historical book in Korea. We can also identify the term 'East Sea' through the royal tombstone of King Gwangggaeto, which was erected in A.D. 414. By contrast, the name of a country 'Japan' came into use in the 8th century, 700 hundred years after the 'East Sea.' Even the term 'Japanese Sea' or 'Japanse Zee' appears first in Kunyu wanguo quantu, A.D. 1602.
Also, looking at the geographical characteristics of the East Sea, four countries including South Korea, North Korea, Japan, and Russia are adjacent to it. Thus, it is greatly inappropriate to name the body of water between these countries after a particular country.
Lastly, although Japan argues that the term 'Japanese Sea' or 'Japanse Zee' was established by the West between the late 18th century and the early 19th century, no authoritative organization in charge of setting international standard territory names has established the term during this period.