Sumdorong Chu incident

The Sumdorong Chu incident was a prolonged military confrontation between India and the People's Republic of China in the Sumdorong Chu valley, a tributary area near the Thag La ridge in what India administers as Tawang district, Arunachal Pradesh, and what China claims as part of southern Tibet.

The crisis began in mid-1986, when Indian patrols found that Chinese troops had established a semi-permanent presence on the southern side of the Sumdorong Chu, an area India considered its own and that had previously been visited seasonally by Indian intelligence teams. India responded under Army Chief General K. Sundarji with Operation Falcon, airlifting brigades to occupy heights overlooking the Chinese position, including Hathung La and the Longro La ridges. By 1987 both sides had built up substantial forces in the eastern sector.

Tensions escalated sharply in the spring of 1987, coinciding with India's grant of full statehood to Arunachal Pradesh in February 1987, which Beijing protested. Western analysts at the time briefly feared a second Sino-Indian war. Diplomacy de-escalated the crisis: Indian External Affairs Minister N. D. Tiwari visited Beijing in May 1987, and Prime Minister Rajiv Gandhi's landmark visit to China in December 1988 reset the bilateral relationship and launched the Joint Working Group on the boundary question.

The standoff had lasting institutional consequences. It directly motivated the 1993 Agreement on the Maintenance of Peace and Tranquility along the Line of Actual Control and the 1996 Agreement on Confidence-Building Measures in the Military Field, which codified troop limits, patrolling protocols, and meeting mechanisms still invoked during later incidents such as Depsang (2013), Doklam (2017), and Galwan (2020). Indian and Chinese troops only disengaged fully from the Sumdorong Chu area in 1995.