Japan took our island, Dokdo when they colonized over Korea. They changed the name of the ocean around Dokdo from East Sea to Sea of Japan, the sovoreignty has been returned, but they still insist that Dokdo is their territory, so Sea of Japan is correct name, which is not true.
According to the international law, sovereignty is only granted depends on who takes the territory by military power. Korean army has controlled Dokdo, so the name of the sea surrounded by the island should be East Sea.
However, a lot of US textbook started choosing 'Sea of Japan' as its name. I need to ask you to correct wrong history.