What caused the decline of the first Bulgarian empire after Simeon I died?

Following the death of Simeon I in 927, the First Bulgarian Empire faced a period of decline driven by both internal instability and external pressures. While Simeon had expanded the empire's borders significantly, his relentless military campaigns to capture Constantinople left the country in a state of near exhaustion.12

The decline was characterized by several key factors:

• Internal Dissension: The empire was weakened by internal divisions, most notably the emergence and spread of Bogomilism, a dualist religious sect that challenged the established Bulgarian Orthodox Church and social order.123
• External Invasions: The state was frequently assaulted by various groups, including the Magyars, Pechenegs, the Rus, and the Byzantines.14
• Military Defeat: The cumulative effect of these pressures led to the fall of the capital, Preslav, in 971, and eventually a decisive defeat by the Byzantine emperor Basil II in 1014. Following the death of Tsar Samuel, the empire lost its independence in 1018 and remained under Byzantine rule for over 150 years.12