Upon winning the first Siege of Rhodes, St John helped to save Christendom. At around the same time, Moslem forces were invading Apulia, in the heel of the boot of Italy. With the survival of the naval forces of St John at Rhodes, the Moslem forces could not depend upon a reliable supply of resources and soldiers by boat. So they could not advance inland to Rome, the seat of Western Christianity.
But there were other, greater reasons for the abandonment of the invasion of Italy. Soon after the siege, in 1481, Sultan Mahommed [Mehmet] II died and there was an immediate power struggle over his throne, dividing the Moslem forces. Also, these forces were virtually stopped at the siege of Otranto in Italy in 1481. The Moslems won, but with heavy losses, and they could not carry on without reinforcements from Turkey. And whether it was the conflict at home or concerns about the navy of St John, the reinforcements never came.
But there were other, greater reasons for the abandonment of the invasion of Italy. Soon after the siege, in 1481, Sultan Mahommed [Mehmet] II died and there was an immediate power struggle over his throne, dividing the Moslem forces. Also, these forces were virtually stopped at the siege of Otranto in Italy in 1481. The Moslems won, but with heavy losses, and they could not carry on without reinforcements from Turkey. And whether it was the conflict at home or concerns about the navy of St John, the reinforcements never came.