What was not a reason for the decline and fall of the Tang Dynasty? Mongol invasion
By the middle of the eighth century, the Tang power had declined. The internal economic instability and subsequent rebellion of An Lushan marked the beginning of the military decline for the Tang empire: "The appreciable system of land distribution, which characterized the early years, disappeared and the peasants, who previously supported the military by paying Forced to move and fight in the border areas, and increasingly, the resources fell to the army's caudillos, who achieved great independence from the central government and greater control of the economy. "An Lushan, commander of three Military regions, favored by the court, revolted against the empire (755-763) and seized Luoyang and Chang'an, beginning with his revolt the definitive decay of central power and dynasty.
The military defeat in 751 by the Arabs in the Talas battle marked the end of the Tang authority in Central Asia.
Finally, bad government, court intrigues, economic exploitation and popular revolts weakened the empire, allowed military chief Zhu Wen to seize the throne to found his own dynasty in 907. Thus, a new Period of fragmentation in the history of China: The period of the Five Dynasties and the Ten Realms.