How soon was the counterattack in self-defense against Vietnam fought?

In 1979 the counterattack in self-defense against Vietnam was launched Vietnam's regional hegemony and the Soviet Union's backing were the fundamental reasons for the outbreak of the war.

First of all, the Soviet Union's strategy in East and Southeast Asia was to cultivate and find proxies in an attempt to grasp the Strait of Malacca and reverse the defensive passivity in the pattern of hegemony, and socialist Vietnam became the first choice.

Secondly, in a post-reunification Vietnam that was riddled with problems, suffering and lacking in resources, the leadership moved away from Ho Chi Minh's post-war strategic center of gravity, and made the wrong choice that was destined to haunt it for decades: to divert attention with the military and the war, and to use the war-trained army and the aid that came from the war for foreign expansion.

Also, Vietnam's terrain is long and narrow, facing the sea and mountains, the strategic environment is extremely unfavorable, there is no space for strategic turnover, especially in the face of China in the north, but in addition to Lang Son, there is no danger to defend, therefore, Vietnam has the annexation of Cambodia and then strategic transfer attempts, at this time in the neighboring countries, there is only the turmoil of the Cambodian can be for the choice of Vietnam, but China does not agree.

Additionally, the United States at this time in the pattern of hegemony in the transition from defense to attack, Vietnam's behavior infringes on China's interests, which is what the United States would like to see, you can use a knife to kill, in order to avenge the shame of the defeat of the war in Korea.

Finally, after China's contact with the United States in 1971, although it possessed the initiative and huge space for strategic survival, it was still unable to get rid of its inherent predicament, and was in urgent need of an event to complete the consolidation of strategic security for its survival and to make a thorough farewell to the decade-long "Cultural Revolution," and the ungratefulness and vengeance of Vietnam made it possible for the Chinese government to fulfill its obligations to China. Vietnam's ungratefulness and repayment of grudges with benevolence have made China whole.