In fact, this issue originated in the 1960s. Before the 1960s, South Korea and North Korea had no dispute that Changbai Mountain belonged to China

Kim Il Sung was born in Changbai Mountain (disputed, but Such was the propaganda of North Korea). In 1962, North Korean representatives held talks with Mao Zedong, the then supreme ruler of China. The North Korean representatives sincerely proposed that Changbai Mountain was the birthplace of the great leader Kim Il Sung. Based on the deep feelings of revolutionary brotherhood between the two countries, they hoped to Changbai Mountain gave up part of its territory to North Korea. Mao readily agreed and ceded about 52% of the territory in Changbai Mountain to North Korea, thus laying the groundwork for territorial disputes between China and North Korea

Although North Korea and South Korea have always been hostile status, but it is more like two hostile regimes in one country. However, this area is very sensitive, which has allowed many major powers to get involved. Therefore, it is not surprising that South Korea has intervened in some territorial disputes between China and North Korea.