For a long time until the middle of the 19th century, Vietnam existed as a vassal state of China. In 1885, after the end of the Sino-French War, Vietnam became a French colony. For nearly a hundred years, there was a constant war in Vietnam. First resisted Japanese aggression, after independence, he fought with the French army for ten years, and from 1961, he fought with the superpower Lao Mei for more than ten years, until the American soldiers left in 1973. After reunification, Vietnam fell in love with fighting and embarked on the road of military exhaustion. Even if it invaded its small neighbors Cambodia and Laos, they dared to move the soil on the head of the tai nian and repeatedly harassed its biggest neighbor.
In the spring of 1979, the People's Liberation Army dispatched 300,000 troops to teach vietnam a harsh lesson to the unrighteous.
In addition to the international situation at that time and the combat experience of its army fighting for decades, there was a more important reason, that is, it had the superpower Soviet Union, an ally.
The Soviet Union, as the big brother of the socialist revolutionary camp, like the great powers in the East, has provided various kinds of assistance to the little brother of Vietnam for decades. Most importantly, in November 1978, just a few months before the Eastern powers taught Vietnam a lesson, the Soviet Union and Vietnam signed a Treaty of Friendship and Mutual Assistance between the Soviet Union and Vietnam. One of the covenants on military matters provides: "As soon as one of the two parties becomes the target of an offensive or offensive threat, the contracting parties will immediately consult with a view to eliminating such a threat and take corresponding and effective measures to guarantee peace and security between the two countries." That is to say, if Vietnam is attacked by a third country, the Soviet Union must fully assist.
But what is well known is that while the great powers in the East were teaching Vietnam a lesson, the Soviet Union, an ally, stood idly by and was unwilling to send troops, regardless of any mutual aid treaty. What is the reason for this?
The Soviet Union had its own difficulties in not sending troops. Although the Soviet Union has more than 4 million troops, we know that the Soviet Union has a very large land area, and these more than 4 million troops are not so rich to be distributed to various regions. In addition to the mainland, a considerable part of the army was also stationed in Eastern Europe.
The second is the issue of strategic focus. During the Cold War, the Soviet Union's strategic focus was on Eastern Europe, with Southeast Asia being secondary. If the Soviet Union had transferred a large number of troops from Eastern Europe, the Eastern European region would have been empty and stretched, and the Soviet Union would not have dared to take this risk. Moreover, with the war situation at that time, the eastern powers sent 300,000 troops, and the Soviet Union needed to help Vietnam, and the army that needed to be dispatched was at least hundreds of thousands.
The third is the issue of the transportation of the army. The only way to connect Eastern Europe to the Far East is the Trans-Siberian Railway, which has limited transport capacity, and if troops are drawn from Eastern Europe to the Far East, transporting huge armies and a large number of weapons and equipment, it will take not a day or two, but a month or two or even longer. According to this calculation, when the Soviet army arrived in Vietnam, it was estimated that the war would have ended long ago, and in fact it took only one month for the eastern powers to teach Vietnam a lesson.
In addition, the afghan problem was imminent, making it impossible for the Soviet Union to withdraw. Afghanistan is located at the crossroads of east-west transportation in Eurasia and its strategic location is very important. In the six years from 1973 to 1979, although the Soviet Union supported several puppet regimes in Afghanistan, the last Amin government purged the more pro-Soviet bannermen in the People's Democratic Party, and in the war between the central government and tribal chiefs everywhere, the tribal chiefs were at a disadvantage, and the Amin government was already difficult to control by the Soviet Union. The biggest fear was that Afghanistan was very likely to fall to the Western camp, so in December 1979, the Soviet Union simply sent more than 100,000 troops to solve the Afghan problem.
For a number of reasons, the Soviet Union was unable to send troops to help Vietnam in the face of the attack of the Eastern powers on Vietnam. But the Soviet Union continued to support Vietnam as strongly as ever in terms of weapons and materiel, and this assistance continued until the late 1980s.