Our spendthrift government waste, and huge deficits and national debt will have the same effect.
Except it is not Venetians, but Congress doing the looting.
Mohammed II only took Constantinople because he secured the services of an expert Christian gunfounder (Urban of Hungary). Urban had offered his services to Constantinople first, but they refused. IMO the Byzantines lost their city because they didn't invest in technology. In the same way, the equally decisive battle of Lepanto was only won because of investment in Naval technology.
Constantinople was sacked by an army consisting of various mercenaries, Venetians and Byzantines. The largest contingent among the troops that sacked Constantinople were themselves Byzantines sacking their own capital city.
The sack of Constantinople occurred in 1203, 250 years before Constantinople fell to the Turks. Pinning the military weakness of 1453 on an incident from 1203 is preposterous.
Most of the treasures of Constantinople were gone well before the Venetians and their allies took the city. Isaac II had looted the treasury before he left the city 8 years earlier, and his successor melted down both Catholic statuary and Orthodox icons for the gold he needed for bribes to keep his tenuous hold on power.
Very little "treasure" was hauled away from Constantinople since very little was left in a city that had been torn by civil strife and kleptocracy for at least a decade.