4 – Weak Military
In the early middle ages, the Byzantine Empire boasted superior military technology to Western Europe and possessed an enormous standing army by the standards of the time. As it was an incredibly wealthy empire, it could afford to hire mercenaries in times of need. In the later stages of the empire, its enemies had caught up regarding technology and the Byzantine army dwindled in size.
The theme system was the empire’s primary method of army recruitment. The empire was divided into several regions, also known as ‘themes.’ Each theme provided the imperial armies with a certain number of soldiers. It was a cheap and efficient method of building an army and allowed the empire to create an enormous force in comparison to its enemies. One example is the theme of Thrakesion which alone provided almost 10,000 men to the army in the early 10th century.
The original system fell apart in the wake of Manzikert; a dramatic collapse since the empire had a force superior to all its enemies in 1025 under Basil II. There was a brief revival under the Komnenian dynasty in the 12th century when Manuel I Komnenos could call upon a standing army of approximately 40,000. This was the last time the Byzantines had an army befitting an empire. When Andronikos I Komnenos was deposed in 1185, it was the end of the empire as a military force.
The new system had required the leadership of a competent emperor; the Angeloi dynasty couldn’t provide it, so the Byzantine army disintegrated. The empire could no longer afford to pay for high-quality mercenaries after being plundered in 1204 after the Fourth Crusade and at this time, it could only produce a pitiful standing army of 4,000. Despite the best efforts of the Palaiologan Dynasty, the Byzantine Empire was doomed; it was just a question of time.