The political and military conditions brought about in the Empire during the 9th century demanded an overhaul of the administrative system. The larger regions, the themes, were divided into smaller units, thus effectively ensuring the defence of the borders.
The partitioning of the themes weakened the influence of their 'strategoi' (generals) who, exercising at one and the same time both political and military authority in the areas of their jurisdiction, had acquired such power that they threatened rebellion against the Emperor himself.
During the 11th century, probably after the destruction in 1018 of the Bulgarian state by Basil II, Bulgaroktonos (the Bulgar Slayer), the themes of Thessalonike and Strymon, which covered the territory of Macedonia, were divided into smaller administrative territories called 'katepanikia'. The new larger theme of Bulgaria, with Ochrid as its chief city, was created at the same time.