Sviatoslav's invasion of Bulgaria

Sviatoslav's invasion of Bulgaria was a conflict beginning in 967/968 and ending in 971, carried out in the eastern Balkans, and involving the Kievan Rus', Bulgaria, and the Byzantine Empire. The Byzantines encouraged the Rus' ruler Sviatoslav to attack Bulgaria, leading to the defeat of the Bulgarian forces and the occupation of the northern and north-eastern part of the country by the Rus' for the following two years.

Source: Wikipedia — Sviatoslav's invasion of Bulgaria (CC BY-SA 4.0)