Territorial evolution of the Ottoman Empire
Suleiman I ( "Süleymān", ; almost always "Kanuni Sultan Süleyman") (6 November 1494  – 5/6/7 September 1566), was the tenth and longest-reigning Sultan of the Ottoman Empire, from 1520 to his death in 1566. Suleiman became a prominent monarch of 16th century Europe. Suleiman personally led Ottoman armies to conquer the Christian strongholds of Belgrade, Rhodes, and most of Hungary. In 1541 he annexed central Hungary while Transylvania became an Ottoman vassal. However rest of the Kingdom of Hungary including western and northern (Upper) Hungary and Croatia still were Habsburgs possessions. Suleiman also conquered Iraq in his conflict with the Safavid dynasty. Under his rule, the Ottoman fleet dominated the seas from the Mediterranean to the Red Sea and the Persian Gulf.
Suleiman I's campaign of 1529
Suleiman's march to Vienna was also an attempt to assist his vassal, John Szapolyai who claimed the throne of Hungary. Suleiman sent his army of 120,000 strong north on the 10 May 1529 . His campaign was marked by speedy success- on September 8 Buda surrendered to the Ottomans and John Szapolyai was installed as King of Hungary. Suleiman then went further taking Gran, Tata, Komárom and Raab so that much of Ferdinand I's gains the previous two years were lost. On 27 September, Suleiman reached Vienna.