China–Vietnam border

An old frontier in the hills

The region’s recorded history begins with the kingdom of Nan Yueh, founded in the 2nd century BC. By the start of the 1st century BC the Han empire had absorbed it, and Tonkin (northern Vietnam) became China’s southernmost province.^[2]

After about ten centuries of Chinese rule, Tonkin broke away in 939. The US Geographer judged that roughly the present boundary seems to have existed between the two states from then on. Chinese forces occupied the country again for two decades after 1407.^[2]

The border hills are home mostly to minority peoples. In 1964 the US Geographer described Akha and Hani near the Laos tripoint, Miao (Hmong) and Yao further east, Tai peoples toward the coast, and Vietnamese around Lào Cai on the Red River and on the narrow coastal plain. Han Chinese were a large share of the population only in the far east.^[2]

France and China draw the line

In the 19th century France looked for a trade route into China. When the Mekong proved impractical, it turned to Tonkin and the Red River, extended its protection over the area in 1882 and 1883, and the next year China agreed to withdraw its troops from Tonkin.^[2]

The 1885 Treaty of Tientsin committed France and China to appoint commissioners to fix the frontier. A convention of 26 June 1887 described the line in detail from the Gulf of Tonkin west to the Black River. A second convention, of 20 June 1895, adjusted the line east of the Black River and completed it to the west.^[2] Commissions marked it on the ground soon afterward.^[2]

The result mostly follows ridge crests: 63.5% of the line runs along water divides, the lines separating one river basin from the next, and 27.5% follows rivers. Straight lines and other features make up the rest.^[2] Near 22°48′N it turns sharply south through karst, limestone country with little surface water, where extra pillars mark the line. That southward stretch ends at the Porte de Chine just north of Đồng Đăng, where the railway crosses. The last stretch follows the Beilun River to the sea; past Móng Cái its northern channel is the boundary.^[2]

War in 1979

In 1964 the US Geographer found the whole line demarcated by at least 285 pillars, knew of no territorial disputes, and noted that Chinese maps drew the border the same way French maps did.^[2] It judged a serious border problem unlikely unless the close relationship between Beijing and Hanoi went bad.^[2]

It did. China objected to Vietnam’s treatment of its ethnic Chinese, its alliance with the Soviet Union and its preparations for war against Cambodia. At 5 a.m. on 17 February 1979 Chinese troops attacked across the border, taking Lào Cai, Cao Bằng and Lạng Sơn. The last Chinese soldiers left Vietnam on 16 March.^[4] Most historians accept estimates of about 26,000 Chinese and 20,000 Vietnamese military deaths.^[4]

Fighting did not stop with the withdrawal. Six major border clashes took place between July 1980 and January 1987. The two countries began talks on normalising relations on 11 August 1989.^[4]

A new treaty and 1,970 markers

Border talks had started in the 1970s and stopped later in that decade. They resumed in the early 1990s.^[3] Both sides agreed to use the 1887 and 1895 France–China conventions as the basis.^[5]

Comparing maps, the two sides agreed on about 900 km of the line. They saw 164 pieces of land along it, about 227 km² in all, differently. The settlement gave about 113 km² of these to Vietnam and about 114 km² to China.^[5] At the Friendship Pass, the line was placed 148 m north of the point where the two railways join.

The treaty was signed in Hanoi on 30 December 1999.^[1] A joint demarcation committee was set up in November 2001, and the two sides settled the last survey questions on 31 December 2008.^[3] They measured the line at 1,449.566 km and planted 1,970 markers: 1,548 main markers and 422 auxiliary ones. Three agreements on the markers, border management and border gates were signed in Beijing in 2009 and took effect on 14 July 2010.^[1]

The border runs through seven Vietnamese provinces and, on the Chinese side, Yunnan and Guangxi.^[1] The line through the Bản Giốc–Detian waterfall follows the middle of the main flow.^[5] A cross-border tourism zone there began trial operations on 15 September 2023 and opened officially on 15 October 2024; visitors cross in groups of up to 20.^[6]