The old rule, first answer: When the Qin state fell, the so-called old Qin people had already fallen into the crowd, and they no longer had the ability and strength to command the people; secondly, they were Qin people, but their hearts had already had nothing to do with the honor and disgrace of the Qin state.
Let's go back to the moment when the Qin state fell, when Liu Bang entered Guanzhong, in fact, the Qin state still had a lot of troops, including hundreds of thousands of troops commanded by Meng Tian and Meng Yi in northern Xinjiang, and in the southern Xinjiang, that is, the current Lingnan region, the Qin general Zhao Tuo led 500,000 troops, until the qin state fell, these two armies did not come back to the rescue.
In fact, these can not blame them, because they are also Qin people, but in the process of getting along with Qin Shi Huang and Qin II, gradually deviated from morality, and the old Qin people gradually broke away from the interest relationship with the Qin state and no longer loyal to the imperial family, then its decline became inevitable.
The "old Qin people" could not restore the country for three main reasons:
1. The "old Qin people" have no strength at all
A large reason why after the fall of the Six Kingdoms was able to restore the country again was because the Qin state had declined, the people's hearts were turned against each other, the monarchs and subjects were at odds, and the number of people who called it a country in ancient times had been exhausted. Then, when Qin destroyed the Six Kingdoms, the important ministers and clans of many countries did not kill them all, and they still had a lot of appeal in the local area, and these appeals gave them the strength to restore the country. Then, when the Qin state was destroyed, the clan and important ministers of the Qin state had long been gone. In general, it is caused by two aspects.

On the one hand, there was a constant killing of those in power of the Qin state, specifically two: Qin Shi Huang and Qin II.
After Qin Shi Huang ascended the throne, he took all the credit on himself, and as a person with a strong desire to control power, he really could not tolerate other people to deprive him of power from him, especially his own clan. Therefore, after qin shi huang reigned, he used two steps to divide all the forces: first, it divided the forces of the old Qin people, first by reusing the Chu foreign relatives to control the government, followed by promoting a wave of Guanzhong generals to control the military power (such as Meng Tian and Meng Yi); in the second step, through the rebellion of Cheng Jiao and the disaster of Yan Yi, the Chu and Han foreign relatives were eradicated, and a number of old Qin forces that held power were eradicated in these two events.
By the time of Qin II, Qin II had done even more desperately, and at the instigation of Zhao Gao, he slaughtered a group of ministers and generals who supported Fusu, including Meng Tian and Meng Yi's father and son, as well as a piece of Qin army generals. In order not to be opposed by the clansmen, especially those elders, Qin II has not been soft on the old ministers, and persecuted many ministers who have been maintaining the Qin Dynasty's clan office, most of whom are mainly old Qin. The most important thing in the clan is that people who are related to themselves are treated by their brothers and sisters, in order to prevent them from coming out to call for opposition to his power and challenge his imperial power, openly using various means, more than 20 brothers and sisters before and after were received by Qin II for a box lunch. The clan and the old ministers were almost destroyed at the hands of Qin II, and the Six Kingdoms were only possible to raise troops to restore the country with clans or old ministers, but under the operation of Qin II, the Qin clan and the old ministers were gone. The famous courtier Li Si was also killed during the reign of Qin II. For his own enjoyment, Qin II vigorously built the Lishan Tomb, the Imperial Palace, the Mausoleum, etc., and the people of Qinzhong were miserable.
The old Qin people were quite dissatisfied with the qin kings' actions, their hearts had already been deeply hurt, even Zhang Handan was not willing to do everything he had for the cause of the Qin state, and finally after being defeated by Xiang Yu, he directly surrendered, and Zhao Tuo and other generals with heavy troops were not willing to come back to rescue the Qin state.
2. The differentiation of Xiang Yu and Liu Bang
Since Qin Shi Huang and Qin II were unpopular, but the power and strength of the old Qin people were still very strong, if they could unite again, it would be a very troublesome thing, so Xiang Yu and Liu Bang also used a series of methods to prevent this kind of thing from happening after they captured the territory of the Qin State, but the methods of the two were different.
Xiang Yu killed the remaining Ying clan, as well as some related old princes and ministers, and when dividing the 18 princes, in order to facilitate the rule and to better handle the relationship between Qin and Qin, Xiang Yu divided the old Qin land into several parts, of which three pieces of land were distributed to the surrendered Qin generals, namely Zhang Handan, Sima Feng, and Dong Xin, allowing them to establish a stable Qin land. At the same time, they belonged to the faction that surrendered, and it was also convenient for Xiang Yu to manage; bashu and Han were divided among the Han kings Liu Bang, who also knew that the Qin people were not easy to manage, and he knew that his strength was inferior to Xiang Yu's and could not be conquered by force, so he and his courtiers came up with the famous "Three Chapters of the Covenant Law". Because the former dynasty used cruel laws, Liu Bang used loose laws and used benevolence to impress the old Qin people, and this measure was recognized and supported by many, many Qin people, that is, to win the hearts and minds of the people.
From the measures of Xiang Yu and Liu Bang, it can be easily analyzed that the Qin people are a powerful fighting force, and they cannot be slaughtered, but can only do everything possible to divide and influence them, only in this way can the Qin state be impossible to restore the country.
3. Long-term implementation of martingale policy
In fact, there is another point that needs to be explained, in the past, the clan and the old ministers almost firmly controlled the power, and the reason why Shang Martin died so tragically was because his policy deprived the upper echelons of the old Qin people who had always supported the Win clan, so that more people at the bottom had the day of their head, after several generations of persistence, the forces of the old Qin people who had been maintaining the Win clan were also gradually disintegrated and destroyed by the rising new forces, which also allowed the later Lü Buwei and Yan Yi to take power.
The old Qin people did not restore the country in the end, which was caused by many factors, so that they only looked at it coldly when the Win clan collapsed. Qin Shi Huang, who had already been buried, did not know how he felt when he saw this ending!
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