From the time of Khan Krum (802-14) Bulgaria threatened Byzantine military while at the same time, falling increasingly under Byzantine ecclesiastical and cultural influence. The Byzantines under Basil II invaded Bulgaria but were defeated by the Bulgars under Czar Samuel near Sofia in 981.
Much of Bulgaria’s existing empire was gradually infiltrated and encompassed by the Byzantines. Its finally succumbed in 1018 with the entire nation of Bulgarian under Byzantine rule of Bail II who was nicknamed Slayer of the Bulgars’. However, he allowed the country practical autonomy.
Members of the royal family and great nobles were co-opted in the Byzantine ruling class. The Byzantine emperor introduced a tax system in the Old Bulgarian kingdom and ordered the Bulgarian patriarchy to be downgraded although may of the Bulgarian aristocrats retained their position as landlord.
The fall of Bulgaria to Byzantine in 1018