Reason one: Emperor Xuanzong of Tang Dynasty ignored the political affairs, indulged in debauchery, lived a luxurious life, and almost never went to court. His control and power over the imperial court was greatly weakened. Therefore, under the corrupt situation that the emperor ignored the state affairs, all parts of the country were more smoggy, and many officials did not go to court. As a result, officials are paid for nothing regardless of North Korea's affairs, and corruption is frequent. So by the time of Xuanzong in the Tang Dynasty, the imperial court had rotted in its bones and was hopeless. Therefore, this laid a great hidden danger for the separatist regime of the buffer region and the rebellion of the people.
The second reason: military measures and methods are wrong, leading to military laxity. Because in the Tang Dynasty, the military strength and military strength of our time were very strong. Therefore, they can all be mercenary and completely ignore the orders of the central authorities. Because they are powerful, they can completely ignore the orders of the court. This also laid a huge hidden danger and foreshadowing for the later separatist situation in the buffer zone. The imperial court gradually lost control of the local army. In addition, the fighting power of the Central Army is far weaker than that of the local government, which leads to the local government being able to surpass the central court. Therefore, the rebellious heart has a long history, which left a solid foundation for the Anshi Rebellion and the Shi Siming Rebellion.
The third reason: the land annexation in the Tang Dynasty was very serious, and the land equalization system destroyed the economic foundation at that time. Due to the implementation of the land equalization system at that time, there was an unbalanced situation of "the rich are connected with the sky and the poor have no place to stand". This makes many people face the situation of losing their land. The people lost their way of making a living, and naturally their resistance to the court intensified. So many people who lost their land joined the rebels. This laid a huge hidden danger for the last large-scale rebellion, and also added a handful of firewood to the formation of the Tang Dynasty from prosperity to decline.