<P> The Byzantine military did not immediately collapse following the disappearance of the theme system . In the 12th century, the Komnenian dynasty re-established an effective military force . Manuel I Komnenos, for example, was able to muster an army of over 40,000 men . This was sufficient to ensure the empire's continued status as a great power for the duration of the Komnenian period . However, the Komnenoi never provided for a future that saw their decisive leadership replaced by incompetence . After the deposition of Andronikos I Komnenos in 1185, the dynasty of the Angeloi oversaw a period of military decline . From 1185 onwards, Byzantine emperors found it increasingly difficult to muster and pay for sufficient military forces, while the failure of their efforts to sustain their empire exposed the limitations of the entire Byzantine military system, dependent as it was on competent personal direction from the emperor . The culmination of the empire's military disintegration under the Angeloi was reached on 13 April 1204, when the armies of the Fourth Crusade sacked Constantinople and dismantled the Byzantine Empire . </P> <P> Despite the restoration under the Palaiologoi, Byzantium was never again a great power on the scale of the past . By the 13th century, the imperial army numbered a mere 6,000 men, while the empire's territories had been reduced to little more than the lands immediately surrounding the Aegean sea . </P> <P> Thus, it is possible to argue that the demise of the theme system was one of the most significant factors in the decline of the Byzantine empire . As one of the main institutional strengths of the Byzantine state, the theme system was never replaced by a viable long - term alternative . This left the empire lacking in underlying structural strengths . The result was an empire that depended more than ever before on the strengths of each individual emperor or dynasty . The collapse of imperial power and authority after 1185 revealed the inadequacy of this approach . </P>

What is the biggest weakness of the byzantine empire