Guo Ziyi
Although the An Lushan Rebellion was finally put down in 763, the Tang was immediately confronted by another threat from the Tibetan Empire. Tibet had benefited from the Tang's prosperous period when trade with the Tang was frequent. During the An Lushan Rebellion, it reached the height of its power, and betrayed the peace treaty with the Tang by supporting the rebels. Weakened by the rebellion, Tang border garrisons were unable to resist Tibetan raids into their territory. Most jiedushi were not ethnically Chinese and had little incentive to defend the Tang Empire, especially when it was ruled by a weak emperor. In response, Suzong re-promoted Guo Ziyi, but only as a military figurehead with no authority, in the hope that merely the threat of sending Guo against them would keep the Tibetans at bay. In 762, a general named Wang Yuanzhi murdered Li Jingzhi, the jiedushi of Shaanxi, claiming that the troops were still so loyal to Guo that they demanded he be reinstated as jiedushi. Suzong was forced to return Guo Ziyi to his former position. When Guo Ziyi arrived, however, instead of thanking Wang he condemned the general for his disloyalty in killing his commander. He also pointed out that such an act disrupted the chain of command, which might embolden the Tibetans to attack. General Wang submitted to his mistakes and committed suicide. Guo Ziyi quickly assumed command of the post and the Tibetans ceased their attacks.