Venetian naval strategy involved maintaining a steady chain of bases along their trade routes to the East, ensuring that its merchants were able to get there and back without being attacked by pirates or Venice's enemies, the Turks.
By the end of the 15th Century, Venice's fleet was occupied trying to force Charles VIII of France out of Italy, at which point, Turkish forces struck without warning. Venice was soundly defeated, losing its Greek outposts. Following that, the Turks managed to invade Venetian territory in Northern Italy. Although Venice was able to keep most of its territory, from that point forward, it would never again be a great naval power.