I will give you some reasons for you why the Japanese sea is the wrong thing. Let's go to the history of the East Sea. East Sea in the West in the early 18th century, since the second half of the seventeenth century map is marked as ' Sea of Korea (mer de coree), or 'I have to Oriental (mer orientale)' '. There is also a map with two names together. Maps, in supposed ¡®eastern sea¡¯ in the UK in 1721, point to donghae in, which means the east sea. But nowdays, Japan urge that Japanese sea is the correct marking on the map. But it is the definite error.
Also there is another reason. Let me introduce. Donghae that area for the East Sea name is historically when Koreans come with more than 20 years. The East Sea after year, Sea of Joseon Dynasty have been more widely used than those in the Sea of Japan.
It means that mark the map to the East Sea is the improtant to our country.