In 1537, commanding a large Ottoman fleet, Hayreddin Barbarossa captured a number of Aegean and Ionian islands belonging to the Republic of Venice, namely Syros, Aegina, Ios, Paros, Tinos, Karpathos, Kasos, and Naxos, thus annexing the Duchy of Naxos to the Ottoman Empire. He then unsuccessfully besieged the Venetian stronghold of Corfu and ravaged the Spanish-held Calabrian coast in southern Italy.^[89] In the face of this threat, Pope Paul III in February 1538 in assembled a ’’Holy League’’, comprising the Papal States, Habsburg Spain, the Republic of Genoa, the Republic of Venice, and the Knights of Malta, to confront Ottoman fleet under Barbarossa.^[90]

In 1539 Barbarossa returned and captured almost all the remaining Christian outposts in the Ionian and Aegean Seas. A peace treaty was signed between Venice and the Ottoman Empire in October 1540, under which the Turks took control of the Venetian possessions in the Morea and in Dalmatia and of the formerly Venetian islands in the Aegean, Ionian, and eastern Adriatic Seas. Venice also had to pay a war indemnification of 300,000 ducats of gold to the Ottoman Empire.

With the victory at Preveza and the subsequent victory in the Battle of Djerba in 1560, the Ottomans succeeded in repulsing the efforts of Venice and Spain, the two principal rival powers in the Mediterranean, to stop their drive for controlling the sea. The Ottoman supremacy in large-scale fleet battles in the Mediterranean Sea remained unchallenged until the Battle of Lepanto in 1571.