One
In the eyes of most people, the "prosperous era of Kangqian" can be said to be the peak of the development of China's feudal society. Indeed, the Qing government under the rule of Kangxi and Qianlong became the most powerful state at that time, and agriculture developed steadily. At that time, Qianlong vigorously encouraged the reclamation of wasteland and the development of agriculture and animal husbandry in a timely manner. At the same time, commerce has also developed rapidly, and various commodities are exported overseas, especially tea, which is welcomed by the nobility. It can be described as a great scene in the country.
At that time, the Qing Dynasty not only had many vassal states, but also was worshiped by many Western countries, which can be said to be compared with the United States now. It was one of the top superpowers at the time.
At that time, it was this "superpower" that had some hidden dangers at that time. From these hidden dangers, it is not difficult to deduce the reason why the Qing Dynasty was invaded by Western powers decades later.

Two
The biggest hidden danger of Kangqian's prosperous world is the economic hidden danger, as recorded in the history books, the people of Kangqian's prosperous world are living very happy and rich. The people were grateful to Kangxi and Qianlong for their wise policies, but they did not know the price behind these "wise policies."
During Qianlong's reign, he tried his best to generate income for the people, and at the same time, imitating his father Kangxi, he repeatedly reduced money and grain taxes. Although this reduced the pressure of the people in this short period of time, it also caused the national treasury to be depleted, at the expense of the national treasury in this prosperous world.
So by the time Yongzheng was in power, he had to reinstate taxes. This is also the reason why Yongzheng is generally unloved by the people, although Yongzheng is very industrious.
Three
There is also the fact that during the "Prosperous Era of Kangqian", the people's lives were too rich, and the spiritual culture could not keep up, resulting in the prevalence of luxury. The situation was like some of the demolition and relocation of upstarts we are seeing now, which was not conducive to the stability of the country at that time.
In addition, the population surge led to the situation of more monks and less meat in the later period. This indirectly led to the subsequent rise in various food and prices, and the vicious circle of "population growth - land reduction - price increase - industrial bankruptcy".
This series of problems arose, and finally the economic decline of the late Qing Dynasty began to decline, and it began to be bullied by Western powers. The failure to eradicate these hidden dangers of the "prosperous world of Kangqian" is the root cause of the subsequent "decline of the Daoxian World"!