Why did Tang Xuanzong die?

After An Lushan launched a rebellion, it matched Chang 'an. In June of the fifteenth year of Tianbao, Emperor Xuanzong of the Tang Dynasty hurriedly led officials and Yang Guifei to flee from Chang 'an to the west. When traveling to Mayi Post (now Xingping West, Shaanxi Province), the imperial army mutinied and killed Yang. Xuanzong was forced to kill Yang Guifei, and the military situation was decided. Since then, Prince Hengli led a part of the imperial army northward to Lingwu (now southwest of Lingwu, Ningxia), and acceded to the throne in July, changing the yuan to virtue and becoming Su Zong. Li Longji led another part of the imperial army south to Chengdu, and was later honored as the Emperor of Heaven. After two years in Germany, Xuanzong returned to Chang 'an from Chengdu and lived in Xingqing Palace (in the south). Eunuch Li Yin persuaded Su Zong to succeed to the throne and won Su Zong's favor. After the Anshi Rebellion was put down, he looked down on himself and was despised by Xuanzong. It was the relationship between Xuanzong and Su Zong that drove Xuanzong to move to the Ganlu Hall of Taiji Palace (in the west). Xuanzong was unhappy in his later years. Buried in Tailing after death.