Sviatoslav I vs Tokhtamysh

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.

Tokhtamysh, with the support of Timur, defeated the rebellious general Mamai and reunified the Golden Horde under his rule. He restored the Horde's authority over the Russian principalities, ending a period of fragmentation.

Tokhtamysh led a campaign against the Grand Duchy of Moscow. He besieged and captured Moscow, burning the city and massacring its inhabitants. The victory reasserted Mongol dominance over the Russian principalities.

Tokhtamysh invaded Timur's territory in Transoxiana, starting a war between the two Mongol rulers. Timur retaliated by invading the Golden Horde, defeating Tokhtamysh at the Battle of the Kondurcha River in 1391.

Timur decisively defeated Tokhtamysh at the Battle of the Terek River. The victory destroyed Tokhtamysh's army and led to the sack of Sarai, the capital of the Golden Horde. Tokhtamysh fled and never regained power.

After his defeat by Timur, Tokhtamysh fled to the Grand Duchy of Lithuania. He was killed in a skirmish with a rival Mongol faction near Tyumen. His death marked the end of the last attempt to reunite the Golden Horde.