The Ottoman Turks, who were followers of Osmans, and who had superceded the Seljuk Turks, had become a major threat to the Byzantine Empire by the mid 15th century, with Constantinople falling to them in 1453, and the Venetians edged out of Greece, except for the Ionian islands, which remained under Venetian control.
The peak of Ottoman power was reached under Sultan Suleyman the Magnificent, who ruled from 1520-66. Suleyman extended his empire throughout the Balkans and Hungary , with his successor, Selim the Sot, adding Cyprus to it in 1570 AD. The conquest of Crete took 25 years, with the capture of this largest of Greek islands in 1669.
The Venetians succeeded in evicting the Turks from the Peloponnese during a three year effort (1684-87) and, and did serious damage to the Parthenon when they advanced on it and lobbed a cannon ball which set off the Ottoman gunpowder magazine. Though the Turks regained control in 1715, their power had long been in decline.