The golden age of Bulgaria opened with the accession of Symeon (893-927) to the throne of the now Christian state. The expansion of the Bulgarian state southwards as a result of continual incursions into imperial territory, as well as the assumption by Symeon of the title of "king and emperor of the Bulgars and Romans" were the chief causes of confrontation with the Byzantine Empire.
Bulgar defeat at Spercheios river
Miniature from the Chronicle of Ioannis Skylitzis,
mid-12th to mid-13th century
After a short-lived peace (tsars Peter and Boris II), an enfeebled Bulgaria was attacked by the Russ and converted into a Byzantine province (971). However, the revolt in 976 of the Kometopouloi (David, Samuel, Moses and Aaron) and the formation of a new state comprising the first Bulgarian state and parts of the territory of western Macedonia incited long-drawn-out bloody conflicts. These ended, after the battle at Kleidion in 1014, with the transformation of Bulgaria into a Byzantine theme (1018) by Basil II, Bulgaroktonos.
Byzantium found it difficult to deal with the Bulgarian uprisings of Peter Deljan and Voitach in the mid-11th century, while in 1185 two brothers, Peter and Asen, established the second Bulgarian state. By the time of tsar John "the Roman Slayer" (1197-1207) this state comprised both Macedonia and Thrace.