What if Constantinople had never fallen to the Turks?

[Decker]

let me clear up what i think Vladimir is saying:

the Byzantines, like the original Romans before them, screwed themselves with all the murderous politics, constant rebellions, over-reaching their boundaries, etc. So in a way, you could say that they caused their own downfall with internal turmoil, and the Turks were simply that little extra tip in the wrong direction needed to destroy it.

So basically you are saying it was a replay of the fall of the Western Roman Empire? Internal conflicts and external threats.