Li Yu vs Sviatoslav I

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.

Sviatoslav led a campaign against the Khazar Khaganate, capturing the fortress of Sarkel and sacking the capital, Atil. This destroyed the Khazar state, ending its dominance over the steppes and opening the Volga trade route to Rus control.

Sviatoslav invaded the First Bulgarian Empire at the request of the Byzantine Emperor. He defeated the Bulgarian army, occupied much of the country, and established his capital at Pereyaslavets on the Danube, threatening Byzantium.

After a three-month siege by Byzantine forces under Emperor John I Tzimiskes, Sviatoslav's army was defeated at Dorostolon. He was forced to surrender, renounce claims to Bulgaria, and withdraw from the Balkans.

Returning to Kiev, Sviatoslav was ambushed and killed by the Pechenegs at the Dnieper Rapids. The Pecheneg chief Kurya made a drinking cup from Sviatoslav's skull. His death ended his expansionist campaigns.