Vietnam, called Annam in ancient times, has become a vassal state of the Central Plains Imperial Court many times, because the small country is remote and densely forested, so the imperial court has too much intersection with it. However, China has sent troops to Vietnam many times in history, but they have failed, do you know what the reason is?
It is said that Qin Shi Huang built the Great Wall to garrison 300,000 troops to prevent the invasion of xiongnu foreign tribes in the north, in addition to sending the great general Zhao Tuo to lead 500,000 Qin troops to the remote southern barbarian lands (present-day Guangxi, Vietnam) and set up camps to defend the town. In 209 BC, when Qin II was in power, due to the accumulation of many years of people's grievances, the peasants in Daze Township revolted, and the rebellion against the rule of the Qin Dynasty quickly resounded all over the world.
At this time, the Qin Dynasty urgently dispatched Zhao Tuo's class to return to the DPRK to support, but unfortunately it was delayed by the wolf soldiers in the Lingnan region with mountain and forest guerrilla tactics, so that they were trapped in it, and eventually could not return to support. With the start of the campaign against the Qin Dynasty and the chu-Han War, Zhao Tuo, who was far away in the Lingnan region, knew that the Qin Dynasty was gone, simply occupied the Lingnan region and the northern part of Annam, established the State of South Vietnam, and was known as the Emperor Wu of South Vietnam, so half of vietnam's territory at that time belonged to the State of South Vietnam.
Later, the Vietnamese considered the State of South Vietnam to be an important dynasty in their history, called the "Zhao Dynasty". By the time of Emperor Wu of the Han Dynasty, the state of South Vietnam was classified as the territory of the Han Dynasty, and the northern region of Vietnam was known as Jiaotong. In the subsequent dynasties, the peoples of northern Vietnam often revolted and became independent, and during the Song Dynasty, Song Taizong began to send troops to northern Vietnam to try to pacify them, but unfortunately the Song army was severely defeated by the Vietnamese army in the Jiaozhi Mountains, and then withdrew to the Song Dynasty, and Song Taizong had no choice but to give up the decision to attack northern Vietnam.
Since the Song Dynasty, Vietnam has officially developed independently, and at the beginning of the Yuan Dynasty, Yuan Taizu could not tolerate Vietnam's independence, so he sent troops to fight, and then the Yuan-Vietnam War began. At first, everyone thought that the Mongol iron hooves could conquer the Central Plains, and a small Annam kingdom was even more important. Unexpectedly, after the Yuan Dynasty army penetrated deep into the Vietnamese territory, it was unexpectedly attacked by the other side, resulting in a fiasco.
After a period of mutual consumption of both hands, Vietnam gradually became unsupported because of small countries, so it signed a truce with the Yuan Dynasty, which became a vassal state of the Yuan Dynasty. During the late Yuan and early Ming dynasties, the Yongle Emperor was confident that he could swallow Annam in one bite, so he once again sent a large army to attack the Vietnamese territory, not wanting to fight for several years without success, all of which ended in failure, which made Vietnam independent again.
Throughout Chinese history, from the Qin Dynasty to the Ming Dynasty, these dynasties have sent troops to fight Vietnam, but most of them have failed. There are three points to summarize:
The first is the problem of terrain environment, from the map to see that northern Vietnam is a tropical jungle, mountains and trees, wild beasts, no road to speak of, which is an advantage for Vietnamese who are familiar with the terrain, can attack the enemy at night, and can quickly sneak into the jungle and disappear without a trace, so that the Central Plains soldiers can not pursue. For example, in the US-Vietnam War during the Cold War, the US military was equipped with advanced equipment and had many advantages, but once it entered the jungle of northern Vietnam, it still had no way to take the Vietnamese army, and eventually it was dragged into it and could not extricate itself.
Second: climate reasons, the whole country of Vietnam belongs to the tropical climate region, especially in the mountains and forests of the miasma is extremely strong, the Central Plains army went deep into the past, day and night to eat, drink and sleep there, resulting in frequent occurrences of water and soil disobedience of soldiers due to climatic problems, and at that time, the doctors were backward, so that small diseases became major diseases, and eventually the soldiers' combat ability was greatly weakened.
Third: the threat from the north, counting the dynasties, its threat is mainly in the northern region, where there are Xiongnu, Turkic, Mongol tribes, etc., so the Central Plains court needs to always pay attention to their invasion. Vietnam is located in the south, there is a remote desolation, many times it is not easy to fight for a long time, usually send a large army to the past, can win, can not fight to lead the division back to the Dynasty, so as not to delay for a long time, will be the northern foreign tribes to take the opportunity to invade the Central Plains.