Li Yu

Under Li Yu's reign, the An Lushan Rebellion was finally crushed after eight years of war. The rebel state of Yan collapsed, and Tang authority was restored over most of the empire, though the dynasty was permanently weakened.

The Tibetan Empire launched a surprise invasion, capturing the Tang capital Chang'an. Li Yu fled to Shanzhou. The Tibetans installed a puppet emperor before being driven out by Tang forces and Uyghur allies. This exposed Tang military weakness.

Li Yu granted amnesty to many rebel generals and allowed them to retain control of their provinces as military governors (jiedushi). This created semi-autonomous fanzhen that weakened central authority and led to future rebellions.

Li Yu negotiated a peace treaty with the Tibetan Empire, establishing a border and ending hostilities for a time. The treaty stabilized the western frontier but did not prevent future conflicts.