On February 17, 1979, hundreds of thousands of Chinese troops crossed Vietnam’s northern border to invade the country, waging a bloody strike along the 600-kilometer border that the two nations share.

Historically, China had previously given Hanoi steadfast support against U.S. forces in the Vietnam War. But their comradeship swiftly began to deteriorate in the mid-1970s, especially when Vietnam joined the Soviet-dominated Council for Mutual Economic Cooperation (Comecon) and signed the Treaty of Friendship and Cooperation with the Soviet Union (USSR) – then China’s greatest rival – in 1978. China called the treaty a military alliance and branded Vietnam the “Cuba of the East,” pursuing hegemonistic “imperial dreams” in Southeast Asia.

In December 1978, Vietnam began a full-scale counter-attack against Kampuchea (today’s Cambodia), whose armed forces had launched a number of unilateral clashes along the Cambodia-Vietnamese land and maritime boundaries between 1975 and 1977, leaving more than 30,000 Vietnamese civilians dead. Vietnam’s incursions into China-friendly Kampuchea, which quickly eradicated the genocidal pro-Beijing Khmer Rouge regime.

But, China’s leader at the time, Deng Xiaoping, did not like it and decided to teach a lesson to the Vietnamese.

On August 25, 1978, Chinese troops crossed the border to Vietnam to assault officers, women, and local people. Le Dinh Chinh, a local policeman, fought back with his bare hands and was stabbed to death by a group of Chinese. Chinh is thus known as the first Vietnamese soldier who fell in Vietnam’s fight against the Chinese invasion. This incident sent an ominous signal of a looming armed conflict between the two brothers. After a few months of serious and careful preparation for a military ground campaign against Vietnam, in the pre-dawn hours of February 17, Chinese spearheads, supported by 400 tanks and 1,500 artillery pieces, concurrently attacked in the direction of Vietnam’s border provincial capitals, when residents living there were still sleeping.

The goal behind China’s attack was to ruin Vietnam’s northern defense system and economic infrastructure and totally destroy most of the villages and major provincial capitals such as Lao Cai, Cao Bang, and Lang Son, but not in a few days as anticipated and scheduled by China. It took three weeks of heavy fighting and severe casualties.

Owning to its large population and the huge disparity in economic and military capacity vis-à-vis Vietnam, the PLA relied on “human waves” of ragtag soldiers and a “scorched-earth” policy to conquer Vietnam. These tactics enabled Chinese soldiers to completely destroy everything in their paths, overrun population centers, and occupy strategically important mountainous areas and high spots along the boundary.

In early March 1979, China suddenly declared its “lesson” to Vietnam was finished and began to withdraw completely on March 16. But, in fact, its campaign was not over. Right after the war, China launched another semi-public campaign that was more than a series of border incidents and less than a limited small-scale war. On the one hand, the PLA maintained a level of steady harassment through artillery fire, intrusions by infantry patrols, naval intrusions, and mine planting both at sea and in inland waterways. On the other hand, China pursued psychological warfare operations to sabotage Vietnam’s attempts to restore its war-torn border economic centres by igniting anti-Vietnamese sentiments among the border ethnic minorities and encouraging them to engage in illicit activities like smuggling.

The 1979 war and armed clashes that flared over border disputes in the subsequent years resulted in a heavy toll. Western estimates the number of Vietnamese dead at 10,000.