The standoff's roots reached back twenty-four years. In October 1962, China attacked Indian positions along the Namka Chu stream, an east-west waterway separating the Thag La ridge from the Hathung La ridge. India's attempt to occupy Thag La had provided the pretext. The defeat was devastating, and for two decades India did not return to the area. Military planners had essentially written off Tawang, the major town to the south, accepting that in any future war they would retreat to the Se La pass and defend from there. A 1980 strategic review changed that calculus. Analysts concluded that surrendering Tawang was unacceptable, and the army determined that the only viable defensive position was along the Hathung La ridge itself - the very terrain India had abandoned in humiliation. Returning to defend it would require confronting the memory of 1962 head-on.

General Krishnaswamy Sundarji, India's Chief of Army Staff, chose speed and audacity. Between 18 and 20 October 1986, codenamed Operation Falcon, Indian forces airlifted troops and vehicles to Zemithang by helicopter. They occupied multiple heights including the Hathung La ridge, seizing the strategic high ground around Sumdorong Chu. The scale of the response was enormous: ten Indian Army divisions and several Indian Air Force squadrons were involved in the broader mobilization. Three divisions were positioned around Wangdung, the contested pasture, supplied and maintained entirely by air. These reinforcements supplemented the 50,000 Indian troops already deployed across Arunachal Pradesh. Both sides dug in, and China called for a flag meeting on 15 November. The standoff held through the winter and into 1987, with neither side willing to blink.

India's decision in late 1986 to grant statehood to Arunachal Pradesh intensified the crisis. China viewed the military buildup and the political act together as deliberate provocation. Beijing's rhetoric sharpened to a tone that reminded observers of the language preceding the 1962 attack, and with the Indian Army refusing to stand down, Western diplomats openly predicted war. The de-escalation began through an unlikely channel. Indian Foreign Minister N.D. Tiwari, traveling to Pyongyang via Beijing in May 1987, carried private messages from Indian leaders assuring China that New Delhi had no intention of escalating further. The first formal flag meeting since 1962 took place on 5 August 1987 at Bum La. Both sides agreed to pursue talks with urgency. The following year, Prime Minister Rajiv Gandhi visited Beijing, the first such visit since Zhou Enlai's trip to India in the 1960s, reopening a diplomatic channel that had been frozen for a generation.

The standoff forced both nations to confront an uncomfortable truth: their undemarcated border was a standing invitation to exactly the kind of crisis that had just occurred. After Gandhi's 1988 visit, Indian political turmoil delayed progress, but in 1993 the two countries signed an agreement to maintain peace along the Line of Actual Control. The agreement introduced the concept of "mutual and equal security," envisioning a thinning of forces based on geography and logistics. Its most ambitious goal was for both sides to agree on a mutually acceptable Line of Actual Control. Decades later, that goal remains unfulfilled. Each nation maintains its own version of the line, and the Sumdorong Chu area itself remains contested. India has since strengthened its infrastructure, acquiring land near the Lungroo La mountain pass and building the strategic road from Lungroo to Yangtse. In 2020, India operationalized the upgraded Kyapho Model Post near the area, equipped with accommodations for eighty personnel. The pasture where intelligence officers once hiked alone is now watched by permanent eyes on both sides of a line that still does not exist on any agreed map.