Tang Xuanzong trusted An Lushan with half the army — the rebellion killed 36 million

Emperor Xuanzong of Tang presided over the golden age of Chinese civilisation. During his early reign (712–741), the empire was the wealthiest and most culturally brilliant on earth — Chang'an was the world's largest city, poetry and art flourished, and the Silk Road linked China to Persia and Byzantium. By the 740s, however, Xuanzong had grown weary of governance. He retired from daily administration and devoted himself to music and his beloved consort Yang Guifei, entrusting the state to her incapable cousin Yang Guozhong.

To guard the northern frontier, Xuanzong appointed a single general, An Lushan, as military governor (jiedushi) of three border circuits — Fanyang, Hedong, and Pinglu — giving him command of 200,000 troops, the finest in the Tang army. An Lushan was a charming Sogdian-Turkic general who made himself indispensable at court. He performed for Xuanzong, flattered Yang Guifei (she adopted him as her son), and was rewarded with ever more authority. Warnings came from the crown prince, senior ministers, even fellow generals. Xuanzong dismissed them all.

In December 755, An Lushan rebelled at Fanyang, claiming a secret edict to remove Yang Guozhong. His army swept south. Luoyang fell within weeks. Yang Guozhong executed commanders on suspicion while the rebels advanced. By July 756, An Lushan's forces had captured Chang'an, the imperial capital. Xuanzong fled to Sichuan with his court and a military escort. The mutinous escort blamed Yang Guozhong and Yang Guifei for the disaster. Yang Guozhong was hacked to death. The soldiers demanded Yang Guifei die too. Xuanzong, helpless, ordered her strangled at Mawei Station. She was thirty-eight.

The rebellion raged for eight years. An Lushan himself was killed by his own son in 757, but the fighting continued under different rebel leaders. The Tang government, under Xuanzong's son Suzong, regained the capitals with help from Uyghur mercenaries and the general Guo Ziyi. By the time peace was restored in 763, the population had fallen by tens of millions through war, famine, and disease. The Tang never regained its former power — military governors became autonomous warlords, and the central government's authority was permanently broken.