Classical Age of the Ottoman Empire
Expansion continued during the first half of the reign of Suleiman I (r. 1520-1566), who conquered first Belgrade (1521) and Rhodes, before invading Hungary in 1526, defeating and killing King Louis II in the Battle of Mohács and briefly occupying Buda. Lacking a king, Hungary descended into civil war over the succession, and the Ottomans gave support to John Zápolya as a vassal prince. When their rivals the Habsburgs began to achieve the upper hand, Suleiman directly intervened by again conquering Buda and annexing it to the empire in 1541. Elsewhere, Suleiman led major campaigns against Safavid Iran, conquering Baghdad in 1534 and annexing Iraq. Ottoman rule was further extended with the incorporation of much of North Africa, the conquest of coastal Yemen in 1538, and the subsequent annexation of the interior.
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.