The decline of the Tang Dynasty began with the Anshi Rebellion. Looking at the history of ancient China, we will find that the decline or demise of most dynasties occurred when the national strength declined and there were faint monarchs. However, before the Anshi Rebellion, the Tang Dynasty was still a prosperous dynasty, and there was also a grand situation of the Tang Dynasty in the kaiyuan dynasty, and many countries in Asia took the Sheng Tang as their suzerainty, and constantly sent merchants or delegations to the Tang Dynasty to study and exchange, which was a prosperous scene.
However, under the prosperity of the world, rebellion broke out. In 755, the Tang Dynasty generals An Lushan and Shi Siming launched a rebellion, known in history as the "Anshi Rebellion", which lasted for eight years, causing the Tang Dynasty to turn from prosperity to decline. So why did the Tang Dynasty have such a large-scale rebellion in its heyday? I think there are four main reasons.
First of all, because the Tang Dynasty built the country with military merit, and the people were proud to join the army, the military strength of the Tang Dynasty was very strong, and the heads of local governments were generally from the military, and even many high-ranking civilian officials had to accept the leadership of military generals in some cases. During the Tang Dynasty, the chief officials of each state were basically military generals, who had considerable power and were able to cultivate their own armed forces by virtue of their local power and prestige. In this way, it lays hidden dangers for future rebellions. If it were a brilliant emperor, these ambitious generals might be suppressed; but if you encounter a faint monarch, it will be difficult to shake these generals. Before the An Shi Rebellion broke out, the rebel generals An Lushan and Shi Siming had been preparing for a long time, and the imperial court knew nothing at all. In fact, the uncontrolled local government of the Tang Dynasty began from the time of the establishment of the dynasty.
Secondly, the outbreak of the Anshi Rebellion lasted for a long time after the Kaiyuan dynasty lasted, at this time the Tang Dynasty had entered the end of the prosperous era, under the cover of the prosperous scene, land annexation was becoming more and more serious, corrupt officials were rampant, local officials oppressed the people for their own interests, and officials protected each other, so that the anger of the people had reached a critical point. Once the local generals rebelled, many people would rally their support. In addition, due to the prosperity of trade, the local government tax revenue in the border area is very high, but the tax revenue handed over to the central government is very small, in addition to satisfying the interests of local officials, but also allows the generals in the border area to have enough capital to build their own army.
Third, because they had been in peace for a long time at that time, the army stationed in the hinterland of the dynasty had not fought for many years, so that their combat effectiveness was low, their spirit was weak, their morale was insufficient, their actions were lazy, and their weapons were not replaced, such an army could not win the battle. The army that launched the rebellion was mainly composed of troops in the border areas, who fought against the nomads for many years, accumulated rich combat experience, brave and fierce, dared to fight, morale was high, and they were invincible. Once a rebellion occurs and the two armies clash, then the rebellious army will certainly be like a bamboo, and the soldiers and horses of the imperial court will fall into the water and collapse into an army.
Finally, after the kaiyuan dynasty, Tang Xuanzong thought that his goal of rejuvenating the country and strengthening the country had been achieved, so he began to be proud and complacent, and indulged in enjoyment, increasingly snubbing the court, and gradually decreasing his attention to the local government, the result of course was that the rebel generals An Lushan and Shi Siming had the opportunity to exploit the loophole.
The outbreak of the An Shi Rebellion was precisely because An Lushan and Shi Siming saw the embarrassing situation facing the Tang Dynasty at that time, as they expected, once the war broke out, the local governments basically did not move, because they were waiting for the opportunity to observe whether the emperor still had enough strength to control the situation in the whole country, which gave An Lushan and Shi Siming enough time to eliminate the central government's concubine army one by one. It is precisely because of the lessons of the Anshi Rebellion that the Song Dynasty after the Tang Dynasty will have many restrictions on military generals, which will eventually lead to the decline of the Song Dynasty.