The Sino-Korean Border Agreement (Chinese: 中朝边界条约; Korean: 조중 변계 조약)[a] was signed by China and North Korea on October 12, 1962, in Pyongyang.

A subsequent agreement followed on March 20, 1964, called the Protocols on the Sino-Korean Border (Chinese: 中朝边界议定书; Korean: 조중 변계 의정서).

However, in 2000, the South Korean newspaper JoongAng Ilbo published leaked copies of the Chinese version of both agreements that are considered by scholars to likely be authentic.

Most legal scholars agree that a unified Korea should attempt to uphold the legitimacy of the agreements and that it is likely China will try to renegotiate the border.

[6][2][3] In addition, Korea's view of Paektu Mountain and its Heaven Lake as its mythic ancestral homeland, first attested to around three centuries ago,[5] has further invigorated the conflict.

However, from the mid-1950s, China experienced numerous border disputes with its neighbors, including but not limited to Burma, the Soviet Union, Pakistan, and India.

This culminated in the 1956 August Faction Incident, in which pro-China and pro-Soviet North Koreans had attempted but failed to remove Kim Il Sung from power, and were subsequently expelled from the country.

[10] Despite this, China adopted a conciliatory stance towards North Korea in order to improve their ties and counter the Soviet Union.

The Chinese Ministry of Foreign Affairs (MFA) took a permissive stance, citing the need to maintain their positive relationship, and encouraged Ambassador Qiao Xiaoguang to not "overreact" to the incident.

[9][4] However, their efforts ended up being delayed due to domestic turmoil caused by the failed 1958 Great Leap Forward, clashes on the Indian border in 1959,[13][4] and cooling relations with the Soviet Union around the time of the Sino-Soviet split.

In March 1960, the Chinese State Council agreed to Jilin's proposal, that the center line of the Yalu River be the border between the province and Korea.

According to a March 14, 1960 State Council document, North Korea constructed highways and houses in contested areas on Paektu Mountain.

[15] According to a 2006 speech Hwang Jang-yop made after he defected to South Korea, Zhou first suggested to Kim Il Sung that they split Heaven Lake in half, around 1958.

[12][4] On February 18, 1962, North Korean foreign minister Pak Song-chol invited ambassador Hao Deqing on a hunting trip, in which he asked to discuss the border dispute.

Shen and Xia speculate that North Korea asked for full ownership over Heaven Lake on Paektu Mountain, and that Chinese negotiations were hampered due to their lack of historical records.

[21] On October 16, 2000, the South Korean newspaper JoongAng Ilbo published a report saying that they had purchased a collection of agreements compiled in 1975 by the Foreign Affairs Office of Jilin province.

[24][d] Also, Heaven Lake atop Paektu Mountain would be divided roughly in half, with North Korea acquiring 54.5% and China 45.5%.

[1][2][4][19][18] According to the leaked text, the Protocols consist of 21 articles that cover a range of topics, including:[24] They divided Heaven Lake using a straight line defined by two border markers: numbers 5 and 6.

It is a falsehood to say that west of the Tumen and Yalu rivers has always been Chinese territory, and that Korea has been a vassal state of China since ancient timesMao reportedly reaffirmed the above ideas on October 7, 1964.

[1][4] However, in 1965, China may have demanded 160 km2 (62 sq mi) of territory on Paektu Mountain during a cool period in their relationship, leading to a series of skirmishes in 1968 and 1969.

On September 16, 1983, fifty-five members of the South Korean National Assembly submitted a resolution claiming sovereignty over the entirety of Heaven Lake.

In 2005, both Koreas sent scholars to Paektu to investigate Chinese claims that the 1712 border marker on the mountain was 20 km (12 mi) south of Heaven Lake.

The scholars disputed the claim, and said they found remains of the Mukedeng Stele that marked the border only 4 km (2.5 mi) southeast of the lake.

[20][19][7] Almost all studies of the topic agree that the legality of succession would depend on the specifics of how North and South Korea merge, with possibilities including absorption, annexation, or a merger between the two states.

[7] They noted that in 2018, Chinese General Secretary Xi Jinping stated that it would be "absolutely impossible to separate any inch of our great country's territory from China".