Since 1354 the Ottoman Turks had been advancing westwards, gaining control of the Black Sea and the Balkans, and conquering the largest city in Europe, Constantinople (and renaming it Istanbul), in 1453, and driving on to the eastern Adriatic. Owing to the exploits of successive Sultans, the Ottomans were, by 1520, the undisputed leaders of the Muslim world. For the rest of the century they played a central role in the politics of Europe.
Suleiman ‘the Magnificent’ (1520-66) expanded Ottoman power further into the Balkans and into the eastern Mediterranean. The effect upon Europe was dramatic. The Holy Roman Emperor, Charles V (in Spain and Italy for most of the 1520s), delegated the administration and defense of his Austrian lands to his brother, Ferdinand. It proved a timely move as Suleiman thrust aside the Hungarian armies at Mohacs, killed King Louis II of Hungary and, three years later, reached the gates of Vienna. Though severe weather conditions led the Ottomans to withdraw after a two-month siege, Ferdinand and his court had been forced to flee, which demonstrated the magnitude of the Ottoman threat to the Holy Roman Empire. In 1532 Charles V himself stood in the way of the largest army ever seen in Europe and succeeded in preventing another siege of Vienna. This, however, was to be a temporary respite and Suleiman’s only military setback. In 1541 the Hapsburgs were forced out of most of Hungary, and six years later at Adrianople agreed to pay the sultan an annual tribute of 30,000 ducats in return for holding a small strip of western Hungary. With the Ottoman frontier 80 miles from Vienna, the Austrian Habsburgs would be treated as a tributary power.
In the second half of the century, the Habsburg emperors strengthened their frontier defenses in anticipation of further Ottoman attacks and in the wake of Suleiman’s death in 1566, Selim the Sot (1566-74) and his successor, Murad III (1574-95), called a halt to the landward advances and. This was because they were feeling the strain of administering their massive empire, a fact reflected by the rising cost of state debts recorded every year after 1592. There would be one more great siege of Vienna in 1683, and fear of the Turks would continue to taint European politics throughout the Renaissance and Reformation periods.