In 1986–87, a military standoff took place between India and China in the Sumdorong Chu Valley bordering the Tawang district, Arunachal Pradesh and Cona County, Tibet. It was initiated by China moving a company of troops to Wangdung, a pasture to the south of Sumdorong Chu that India believed to be its territory. The Indian troops stood their ground on the neighbouring Longro La ridge and both the sides moved a large number of troops to the border. The crisis was diffused after the visit of Indian External Affairs minister to Beijing in May 1987. The standoff gave rise to fears of escalation. Subsequently, India and China formulated agreements for managing future border tensions.

Sumdorong Chu is a tributary of the Nyamjang Chu river that flows along the disputed Sino-Indian border between the Tsona County of Tibet and the Tawang district of Arunachal Pradesh. It originates in the Tokpo Shiri Glacier, about 7–10 kilometres east of Nyamjang Chu, and flows down to the river. Its junction with Nyamjang Chu is to the north of that of Namka Chu, another contested river valley, by about two kilometers.