Triv! As mailinutile2 suggested, just have the 4th Crusade before 1204 and have them hang on to it.


Not letting Venice go would hardly do the job, because, well, Byzantium managed to lose Northern Italy, not once, but twice. Byzantium was quite the world champeen at losing turf ;-). Trust me, it doesn't matter how many times you reannex that part of Italy - they'll just lose again the next time an idiot has the throne, as they lost the rest of the Empire.
Basileus Giorgios
Venice in OTL drained the Empire's lifeblood, and acted first as a passive parasite through the Komnenid period, and then as an active vampire in the slow, sad years of the thirteenth and fourteenth centuries. Make no mistake about it, Venice will protect her own interests, and not those of any "schismastic Greeks"- and this means an OTL result of ultimately partitioning a divided Roman Empire for her own ends.
...er, was there really enough Empire left for it to be called "partitioning?"


Sorry - I couldn't resist.
Well, what do you expect? The Roman Empire was an unchecked monarchy, and Venice an oligarchic republic.