The Chinese invasion of Vietnam in 1979 has lessons for India. The same fear is stalking the Chinese, that India is getting into some sort of a military alliance with the West, especially the USA to its geo-strategic detriment in the region. Also the fact that the “spittist” Dalai Lama is allowed exile in India and India’s tough stance in Arunachal is being viewed very suspiciously by the Chinese.
Hence, a look at recent history. Feb 1979 : China & Vietman.
China's relations with Vietnam began to deteriorate seriously in the mid-1970s. After Vietnam joined the Soviet-dominated Council for Mutual Economic Cooperation (Comecon) and signed the Treaty of Friendship and Cooperation with the Soviet Union in 1978, China branded Vietnam the "Cuba of the East" and called the treaty a military alliance. Incidents along the Sino-Vietnamese border increased in frequency and violence. In December 1978 Vietnam invaded Cambodia, quickly ousted the pro-Beijing Pol Pot regime, and overran the country.
China's twenty-nine-day incursion into Vietnam in February 1979 was a response to what China considered to be a collection of provocative actions and policies on Hanoi's part. These included Vietnamese intimacy with the Soviet Union, mistreatment of ethnic Chinese living in Vietnam, hegemonistic "imperial dreams" in Southeast Asia, and spurning of Beijing's attempt to repatriate Chinese residents of Vietnam to China.
In February 1979 China attacked along virtually the entire Sino-Vietnamese border in a brief, limited campaign that involved ground forces only. The Chinese attack came at dawn on the morning of 17 February 1979, and employed infantry, armor, and artillery. Air power was not employed then or at any time during the war. Within a day, the Chinese People's Liberation Army (PLA) had advanced some eight kilometers into Vietnam along a broad front. It then slowed and nearly stalled because of heavy Vietnamese resistance and difficulties within the Chinese supply system. On February 21, the advance resumed against Cao Bang in the far north and against the all-important regional hub of Lang Son. Chinese troops entered Cao Bang on February 27, but the city was not secured completely until March 2. Lang Son fell two days later. On March 5, the Chinese, saying Vietnam had been sufficiently chastised, announced that the campaign was over. Beijing declared its "lesson" finished and the PLA withdrawal was completed on March 16.
Hanoi's post-incursion depiction of the border war was that Beijing had sustained a military setback if not an outright defeat. Most observers doubted that China would risk another war with Vietnam in the near future. Gerald Segal, in his 1985 book Defending China, concluded that China's 1979 war against Vietnam was a complete failure:
"China failed to force a Vietnamese withdrawal from [Cambodia], failed to end border clashes, failed to cast doubt on the strength of the Soviet power, failed to dispel the image of China as a paper tiger, and failed to draw the United States into an anti-Soviet coalition." Nevertheless, Bruce Elleman argued that "one of the primary diplomatic goals behind China's attack was to expose Soviet assurances of military support to Vietnam as a fraud. Seen in this light, Beijing's policy was actually a diplomatic success, since Moscow did not actively intervene, thus showing the practical limitations of the Soviet-Vietnamese military pact. ... China achieved a strategic victory by minimizing the future possibility of a two-front war against the USSR and Vietnam."
After the war both China and Vietnam reorganized their border defenses. In 1986 China deployed twenty-five to twenty-eight divisions and Vietnam thirty-two divisions along their common border.
The 1979 attack confirmed Hanoi's perception of China as a threat. The PAVN high command henceforth had to assume, for planning purposes, that the Chinese might come again and might not halt in the foothills but might drive on to Hanoi. The border war strengthened Soviet-Vietnamese relations. The Soviet military role in Vietnam increased during the 1980s as the Soviets provided arms to Vietnam; moreover, Soviet ships enjoyed access to the harbors at Danang and Cam Ranh Bay, and Soviet reconnaissance aircraft operated out of Vietnamese airfields. The Vietnamese responded to the Chinese campaign by turning the districts along the China border into "iron fortresses" manned by well-equipped and well-trained paramilitary troops. In all, an estimated 600,000 troops were assigned to counter Chinese operations and to stand ready for another Chinese invasion. The precise dimensions of the frontier operations were difficult to determine, but its monetary cost to Vietnam was considerable.
By 1987 China had stationed nine armies (approximately 400,000 troops) in the Sino-Vietnamese border region, including one along the coast. It had also increased its landing craft fleet and was periodically staging amphibious landing exercises off Hainan Island, across from Vietnam, thereby demonstrating that a future attack might come from the sea.
Low-level conflict continued along the Sino-Vietnamese border as each side conducted artillery shelling and probed to gain high spots in the mountainous border terrain. Border incidents increased in intensity during the rainy season, when Beijing attempted to ease Vietnamese pressure against Cambodian resistance fighters.
Since the early 1980s, China pursued what some observers described as a semi-secret campaign against Vietnam that was more than a series of border incidents and less than a limited small-scale war. The Vietnamese called it a "multifaceted war of sabotage." Hanoi officials have described the assaults as comprising steady harassment by artillery fire, intrusions on land by infantry patrols, naval intrusions, and mine planting both at sea and in the river ways. Chinese clandestine activity (the "sabotage" aspect) for the most part was directed against the ethnic minorities of the border region. According to the Hanoi press, teams of Chinese agents systematically sabotaged mountain agricultural production centers as well as lowland port, transportation, and communication facilities. Psychological warfare operations were an integral part of the campaign, as was what the Vietnamese called "economic warfare"--encouragement of Vietnamese villagers along the border to engage in smuggling, currency speculation, and hoarding of goods in short supply.