Why did the gate valve system prevail in Wei, Jin, Southern and Northern Dynasties, but basically ended in Sui and Tang Dynasties?

The gate system is a special form of feudal hierarchy. It was formed in the Eastern Han Dynasty and prevailed in Wei, Jin, Southern and Northern Dynasties. There are two pillars outside the gate of the ancient official in China. The one on the left is called "valve" and the one on the right is called "reading", which is used to post merits. Later generations called the people who have been officials for generations "valve reading", "door family" and "gentry". After Emperor Wu of the Western Han Dynasty, Confucianism was advocated, and bureaucrats started with Confucian classics. They give lectures, and one's intimate party followers and students are all over the world, forming a social force. His son Sun Chengjia continued to be an official. Over time, by the middle of the Eastern Han Dynasty, a large family of officials appeared.

Form:

The most important one is Liu Xiu, the founder of the Eastern Han Dynasty, who made great contributions to Da Zhuan after the founding of the People's Republic of China and created the first batch of rich people.

Development: At the end of the Eastern Han Dynasty, a large number of farmers went bankrupt and land annexation was serious. Resulting in a large number of big landlords. During the Three Kingdoms period, due to the war, a large number of farmers went bankrupt, and land annexation was further intensified. Although the rulers took some measures to alleviate it, the substantive problems were not solved. Wei's military and political system was only temporarily eased, but it was finally taken over by the big landlords and powerful men. The late Eastern Han Dynasty and the Three Kingdoms period were the periods of the development of gate valve system. Another manifestation of the development of the gate system in this period is Wei's talent selection system and the nine-product system, which caused the ruling class to be completely controlled by the big landlords and tyrants.

The Southern and Northern Dynasties was the peak of the development of the gate valve system. Big landlords and powerful people control most of a country. Sometimes emperors have to be controlled by big landlords and powerful people. They occupy a dominant position in the country's economy and politics, which also creates a strict hierarchical system of "no poverty for the top grade and no family for the bottom grade". The special status has caused a large number of extravagant and dissolute people and planted seeds for the decline of the door-to-door system.

Decline: Sui and Tang Dynasties: In order to consolidate the state power, the rulers vigorously cracked down on the gentry, and in order to promote the poor, they adopted the imperial examination system. The rise of the imperial examination promoted the decline of the gentry system.