From the An Lushan Rebellion.
When the emperor fled to Sichuan with his concubine, the unfortunate Yuhuan had to bear the suffering that should not have been borne by her. Thus, Bai Juyi lamented - yellow dust scattered winds, cloud stacks haunted climbing Jiange. When Li Longji arrived at Jiange, he was no longer the emperor, but he still missed Yang Yuhuan.
The An Shi Rebellion (安史之乱) was a war waged by Tang generals An Lushan (安禄山) and Shi Siming (史思明) after they betrayed the Tang dynasty in the late Xuanzong (玄宗)(玄宗)and early Daizong (代宗) dynasties of the Tang Dynasty (唐代宗) in the early Tang dynasty of China (from Dec. 16, 755, to Feb. 17, 763). This civil war led to a massive loss of population and a sharp decline in the power of the Tang Dynasty.
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Background Summary p>Background
The Tang Dynasty was characterized by the "Rule of Zhenguan" of Emperor Tang Taizong, the "Rule of Yonghui" of Emperor Tang Gaozong, and the "Rule of Zhenguan and Kaiyuan" of Emperor Wu Zetian. The Anshi Rebellion had a major impact on the development of the Tang Dynasty.
The causes of the An Shi Rebellion were manifold, a concentrated reflection of various social contradictions, mainly including the contradictions between the ruling class and the people, the internal contradictions within the rulers, and the contradictions between the central government and the local ruling forces, and so on.
The intensification of internal contradictions within the ruling class was the direct cause of the An Shi Rebellion. In the late reign of Emperor Xuanzong of the Tang Dynasty, Li Linfu, a treacherous prime minister with a "honeyed mouth and a sword in his belly," held the reins of government for nineteen years. During his time in office, he ostracized dissenters and cultivated a clique to control the government.
Successor to his brother Yang Guifei Yang Guozhong, is a "disregard for the world's success or failure", only to follow the selfish misrepresentation of the country, he public bribery, jealous of the wise and domineering, arrogant and domineering, unbeatable.
Baidu Encyclopedia - The An Shi Rebellion