Nomenclature
Within the 19th Century, the sea was known as the Mer de Corée (Sea of Korea) in French, and was one of the three main seas within East Asia, the other two being Mer du Japon (Sea of Japan) to the north and Mer de Chine (Sea of China, today the South China Sea) to the south.
Until World War II, the sea was referred to as 東支那海 (Higashi Shina Kai; "East Shina Sea") in Japanese. In 2004, official documents of the Japanese Foreign Ministry and other departments switched to the name 東シナ海 (pronounced the same), which has become the standard usage in Japan.
Read more about this topic: East China Sea