Byzantine conquest of Bulgaria
From c. 970 until 1018, a series of conflicts between the Bulgarian Empire and the Byzantine Empire led to the gradual reconquest of Bulgaria by the Byzantines, who thus re-established their control over the entire Balkan peninsula for the first time since the 7th-century Slavic invasions. The struggle began with the incorporation of eastern Bulgaria after the Russo-Byzantine War (970–971).
Source: Wikipedia — Byzantine conquest of Bulgaria (CC BY-SA 4.0)