We all know that Shang Yang's political reform strengthened the national strength of Qin and laid the foundation for the unification of the six countries. However, after the reunification of the country, Qin Shihuang did not recuperate and actively changed the ruling system, which was still a set of harsh laws during the war.
In addition, Qin Shihuang was overjoyed, paid attention to personal enjoyment, and recruited people from all over the world to build the Great Wall, the Equator, the Epang Palace and the Mausoleum, seeking the elixir of life, which also caused a great burden to the lives of ordinary people. Even after the death of Qin Shihuang, these things continued. Finally, Chen Sheng and Guangwu rose up in osawa Township and shouted the slogan "Governors would rather have seeds", which opened the prelude to the demise of the Qin Dynasty.
Of course, it must be mentioned that Zhao Gao and Reese appointed by Qin Shihuang are not good goods. After his death, he supported such a bad king as Hu Hai and killed Prince Fu Cha and General Meng Tian, which greatly weakened the internal strength of the Qin Dynasty and undoubtedly destroyed the Great Wall.
Therefore, after Liu Bang unified the whole country, he actively learned the lessons from the demise of the Qin Dynasty, abolished the strict rule of Legalists, and adopted the technique of Huang Lao for quite a period of time, doing nothing, so that the people of the world could recuperate and make the country stable and prosperous quickly.
The reasons for the demise of the Qin Dynasty are largely consistent with those of the Sui Dynasty. Rulers do not pay attention to the people, and all kinds of heavy corvee and harsh bureaucracy make people have no way out, thus losing the basis of rule.