[afuturegovernor]

The Byzantine Empire had been weaken by Islamic armies on the East and Catholic Christian armies on the West for several centuries. Its too bad the city had to fall to the Turks.

[Frumious Bandersnatch]

Actually, the Byzantines were themselves, in great measure, responsible for their own fall. Their corruption was so endemic it gave rise to a new word to the lexicon - byzantine.

[Question_Assumptions]

Let's not forget that the Byzantine Empire was weakened by its own internal infighting. A lot of Turks were brought in as mercenaries by various Byzantine factions.