China–Mongolia border

It runs from west to east between the two tripoints with Russia for 4,630 km (2,880 mi), with most of the boundary area lying in the Gobi Desert.

From there the border veers to the north-west and then west, utilising the Khalkhyn Gol river for a stretch before running through Buir Lake, and then turning sharply to the north-east up to the eastern Russian tripoint.

Russia had expanded far into Siberia during the course of the 17th century, bringing it into conflict with Qing China, which at that time ruled over Outer Mongolia.

[3] Disputes soon arose over the border, notably over the gold-rich Baytik Mountains in 1947, and further work on boundary delimitation was hampered by the Chinese Civil War.

[3][5] With the Communists in power in China from 1949, relations with Mongolia steadily improved, and the two countries signed a treaty on 26 December 1962 delimiting their common frontier.