During the Vietnam War, the mainland provided a lot of aid to Vietnam, but after the end of the Vietnam War, Vietnam colluded with the Soviet Union and fought a rake and took revenge. In the end, the mainland, with no patience and no retreat, launched a counterattack against Vietnamese self-defense. In just 28 days, lang son was conquered and pointed directly to Hanoi. At that time, Vietnam had no danger to defend, and in this situation, the mainland chose to withdraw its troops and not occupy a place.
First of all, at that time, Vietnam and the Soviet Union signed the "Soviet-Vietnamese Treaty of Friendship and Cooperation", the most important point of the treaty was that when Vietnam was attacked, the Soviet Union had to fully support Vietnam. On the one hand, the Soviet Union used Vietnam as a springboard for its power in Southeast Asia, and cooperation with Vietnam allowed the Soviet Navy to gain valuable overseas bases in Southeast Asia. On the other hand, Vietnam must also rely on the power of the Soviet Union to achieve the goal of hegemony in Southeast Asia.
It was precisely by virtue of this "Soviet-Vietnamese Treaty of Friendship and Cooperation" that Vietnam dared to wantonly violate our borders. And what we had to do was to catch Vietnam off guard in a short period of time, eliminate its living forces, teach and deter the other side. The mainland chose to withdraw its troops within 28 days, in fact, to tell Vietnam that the mainland has the strength to take Hanoi in a short period of time. In addition, the withdrawal of troops in a short period of time also made it too late for the Soviet Union to make an effective response, when the main forces of the Soviet Union were in Europe against NATO, and it was still difficult to gather a large number of troops in the inaccessible Far East, so in the end the Soviet Union did not have time to respond.
Another important reason is that the mainland has learned the lessons of the United States and does not want to turn the self-defense counterattack war against Vietnam into a long-term war, the military strength of the United States is very strong, in the Vietnam War are deeply mired in the quagmire and can not extricate themselves, even if we occupied a large area at that time, the Vietnamese are very good at guerrilla warfare, it will also consume our strength. Moreover, the purpose of the mainland's counterattack at that time was not to occupy their places, but to eliminate the strength of several of its divisions in a short period of time, to show its combat ability, and to defend ourselves from aggression.
And we also have to look at the situation at that time, Vietnam is a low-latitude country, its climate is special. In addition, northern Vietnam is full of mountainous jungles and steep terrain. Our withdrawal was on March 16. Because Vietnam is about to enter the rainy season, once it enters the rainy season, the complex mountain jungle will be more muddy and slippery, in this case, the mainland's heavy weapons can not be used, and the Vietnamese guerrillas can use their familiarity with the terrain to carry out guerrilla warfare, so the mainland chose to withdraw its troops in such a short period of time.
It turned out that the mainland's choice at that time was very wise, and it was in the same year of the counterattack against Vietnamese self-defense, that is, in 1979. The Soviet Union invaded Afghanistan, although the military strength of Afghanistan is very weak, but this war has also been fought for a full 10 years, and has become a major inducement for the collapse of the Soviet Union, the mainland chose to withdraw its troops in a short period of time, not only to avoid unnecessary casualties, but also effectively punish the invaders, it is a very wise choice.