And I think all the neoconservatives, including VDH, have a fanciful view of republican government. Civil societies create republics, not the other way around. Venice was not great because it was a republic. It became a republic because it was great.
The Sultan’s embargo on trade didn’t last all that long, but you are correct that the fall of Constantinople played a major role in the decline of Venice. Constantinople was the epitome of the realtor’s law: Location, Location, Location. It controlled the land and sea routes to the east. While in the late Byzantine period, Venice had more or less exclusive trade rights through Constantinople (the Genoese also had some rights). Venice backed Byzantium against the Turks, so after the fall the Turks chose to freeze out the Venetians. However, while the Turks may not have been naturals at commerce they weren’t stupid; they did re-open the trade. It’s just that they let in a new set of players, most notably the French.
When the French were able to do business in Constantinople as well as have access to the Atlantic trade, Venice was doomed. The Venetians were only prosperous as long as they were the only game in town.
He is very aware. Read his book, one of his first, “ The Other Greeks”