The international official name of this marginal sea is "Sea of Japan", and "East Sea" is merely a local name used in ONLY Korea Peninsula. Some Koreans insist that the name "Sea of Japan" is a heritage of Japan's colonial policy and should be changed. However, their insistence is completely groudless and FALSE. Prof. Hideo Kawai (Kyoto University) investigated maps published in Europe and America, and showed that the name "Sea of Japan" had already been used in the 17th century by Europeans. "Sea of Japan" had already become popular in the 19th century even in Europe and America, and been used much more frequently than "Korea Sea". It is obvious that the name "Sea of Japan" got fixed internationally before 1910, when Japanese colonization of Korea began. It has nothing to do with the international spread of the name "Sea of Japan".
Furthermore, the name "Sea of Japan" is the most appropriate name from the geographical point of view. About a half of the marginal sea on the earth are named after the island or archipelago or peninsula that separates the sea from the surrounding ocean (For example, Andaman Sea, Irish Sea and Sea of Japan). Each marginal sea has its own unique geographical and oceanographical character because of the existence of the island(s) or peninsula that separates the sea from the open ocean. If the island(s) or peninsula didn't exist, there wouldn't be a marginal sea that should be given a name. Therefore, the above-mentioned nomenclature is the most appropriate geographically. On the contrary, "East Sea" is inappropriate as an international geographical name. "East" is a word only indicating the direction, and the viewpoint is unknown. As a result, you can say that the name "Sea of Japan" is the most appropriate as an international geographical official term. Even Russians and Chinese are for "Sea of Japan" and use it. ONLY a part of Koreans deny it, however, their insistence is completely groundless. Those who ignore the clear truth will blot their own honor.