Emperor Qianlong was the emperor who actually controlled the government for the longest time in China's feudal history, and was also the longest-lived emperor. Emperor Qianlong was one of the founders of the "Kangqian Prosperous Era". However, in the later period of his reign, the Qing Dynasty turned from prosperity to decline, and there were three main reasons for this phenomenon. Economically, the Qianlong Emperor's policy of "valuing agriculture and suppressing business" in the past seriously hindered the budding development of capitalism. Daxing"** is to put everyone in danger of the scholar class. 
1. Political reasons (1) The implementation of the policy of closing the country to the outside world has changed the trend of China's history, and the once powerful Chinese nation has since become backward. In the 22nd year of Qianlong, the policy of "one-stop trade" was implemented. According to the regulations, foreigners can only do it in Guangdong**. The reason why Emperor Qianlong stipulated this was because the British merchants at that time had repeatedly violated the laws of the Qing Dynasty when they were trading with China, in addition, the Japanese and European colonists often invaded the coastal areas of our country, which seriously affected the rule of the Qing Dynasty. Therefore, the customs tax in Zhejiang was increased, hoping to make British merchants leave Zhejiang, but this policy had little effect, and the Qing Dynasty ordered the closure of the customs in Fujian, Zhejiang, and Jiangsu, and only retained Guangzhou's foreign trade. At the same time, the implementation of this policy was also closely related to the domestic situation at that time. Although the Qing Dynasty overthrew the Ming Dynasty, it did not completely sweep away the Ming Dynasty forces, and there were still many anti-Qing forces in the south. In the south, they co-opted many landless peasants to join the uprising. During the Ming Dynasty, many southern people immigrated to various parts of Nanyang, and these people still identified with the rule of the Ming Dynasty. The rulers were afraid of the invading forces at home and abroad. The implementation of this policy, to a certain extent, maintained the rule of the Qing Dynasty, but this policy strictly hindered the country's economic and cultural development. In addition, this policy also brought a serious crisis to China, and the closed environment made China more and more backward, and finally led to the country's degeneration into a semi-colonial and semi-feudal society. 
2) The political situation of "re-Manchu and suppressing Han" As a minority regime, if the Qing ** wanted to rule the whole of China, it must unite the landlords and intellectuals of the Han nationality. In this way, the Qing ** was able to exercise a strong rule over the whole of China. Emperor Qianlong also followed this policy, but he was still wary of the Han Dynasty**, and he was also full of mustard for the Green Camp Army, an armed force composed of Han Chinese. Hang Shijun, a famous historian of the Qing Dynasty, commented on Qianlong, saying, "The governors of the world are full of Han and Han people, and the governors are not Han Chinese." "At that time, the local government implemented a system of governors, and each province had a governor to take charge of the administrative affairs of each province. The governor oversaw the local government as well as the military. A governor can only govern one province, whereas a governor can administer multiple provinces. In the Qianlong period, most of the civil and military ministers were Manchus, and only a few Han ministers such as Zhang Tingyu held important positions, and these people only served in the inner court and did not have great decision-making power. Under such circumstances, the contradictions between the Manchu and Han nationalities will naturally become deeper and deeper, which is extremely unfavorable to national reunification. 2. Economic reasonsDuring the reign of Emperor Qianlong, the country's economic development was extremely prosperous, the population of the country reached 300 million, the treasury was also extremely rich, and the handicraft industry was extremely developed. However, Emperor Qianlong did not change the feudal society's policy of emphasizing agriculture and suppressing commerce during this period, but paid more attention to agricultural production. Under these circumstances, the germ of capitalism, which had arisen during the Ming Dynasty, had not developed and grown. 
3. Cultural reasons (1) Daxing "**After the Qing Dynasty entered the customs, the remnants of the Ming Dynasty were not cleared, so the rulers were very jealous of it. Although in the process of feudal historical development, there have been cases of ethnic minority regimes unifying the Central Plains, but all along, Han culture has always been in a strong position compared with minority culture. Dynasties may be overthrown, but culture has never died. The rulers of the Qing Dynasty may have seen the powerful power of culture, and carried out large-scale ** and murder of literati. Qianlong period "** is very serious, at that time there have been sporadic uprising movements, the Qianlong Emperor increasingly felt the resistance of the people, in this case, he tried to strengthen the rule of thought, hoping to deter intellectuals and the people involved in the civil uprising movement through the cruel criminal law, it is estimated that the Qianlong Dynasty reached more than 130 cases, many of them were just chasing the wind and catching shadows were added to the trumped-up charges. At that time, people often made false accusations against each other because of personal grievances. They are afraid of being implicated if they don't handle it properly, so they often deliberately exaggerate. Under these circumstances, the literati did not dare to express their own opinions on historical politics, which was extremely detrimental to the development of a dynasty. (2) The rigidity of the Bagu Shishi After the Sui and Tang dynasties, the imperial examination system became the most important talent selection system in the country, but in the Ming Dynasty, the content of the imperial examination system tended to be rigid and stagnant, and the Bagu Wen became the prescribed style of the imperial examination. The prevalence of this talent selection system led to the ideological rigidity of the world class at that time, and the development of the entire social system stopped, making the original thoughtful imperial examination a tool for scholars to enter the officialdom. During the period of Emperor Qianlong, Bagu was seriously ossified, and he did not change this talent selection system, and it was difficult to reuse the selected Han people, so during his reign, social thought was extremely inactive and lacked the power to promote social development. 
Fourth, Emperor Qianlong's personal reasons (1) Many patrols cost national strength Emperor Qianlong was an emperor who liked to travel around a lot, and during his reign, he made 6 southern tours and 5 western tours. In addition, he has also been to Shandong, Shengjing and other places many times, and according to statistics, he has had more than 150 lucky tours in his life. This kind of large-scale lucky tour is different from a private visit to Weifu, which requires a lot of money. This was undoubtedly a great burden on the people at that time. (2) During the Qianlong period, a number of imperial gardens were expanded or built, forming a royal garden pattern of "three mountains and five gardens", in addition to this, the Qianlong Emperor also ordered the expansion of the Forbidden City and other buildings. The craftsmanship used in the construction process is extremely elaborate and the cost is naturally very large. This left a lot of artistic crystallization for later generations, but it brought a burden to the people at that time. This is also an important reason why the Qing Dynasty turned from prosperity to decline during the Qianlong period. (3) ArroganceWe must admit that Emperor Qianlong made great achievements in the early period of his reign, but this led to the arrogance of Emperor Qianlong's heart. At that time, Britain had sent a Macartney mission to China, hoping to establish ** relations with China. Just when the mission met with Emperor Qianlong, a serious dispute arose between the two sides, and Emperor Qianlong thought that the act of sending the British delegation to visit was a tributary act of the subject countries in the past, but in the eyes of the mission, they represented the British country, and this diplomatic activity was an exchange between two countries on an equal footing. Because of etiquette, Emperor Qianlong was very dissatisfied, but he did not know that he was about to miss the opportunity to understand the outside world. 
In addition, when the mission came to visit China, it also brought many gifts, among them, there is an atlas that records the development of the British Industrial Revolution, as well as many achievements of the Industrial Revolution, which can be said to be the essence of British social development at that time, but the Qianlong Emperor did not care about this, in his opinion these things are just "miracles and obscenities". In this way, China lost the opportunity to rapidly increase its productivity. Summary: Although the Qing Dynasty began to decline from prosperity to decline, we cannot attribute the reason for this result to Emperor Qianlong alone. The formation of this situation has its inevitability, which the feudal dynasty will inevitably experience in the process of development.