Some Hungarian nobles proposed that Ferdinand, who was the ruler of neighboring Austria and tied to Louis II's family by marriage, be King of Hungary, citing previous agreements that the Habsburgs would take the Hungarian throne if Louis died without heirs. However, other nobles turned to the nobleman Ioan Zápolya, who was being supported by Suleiman. Under Charles V and his brother Ferdinand I, the Habsburgs reoccupied Buda and took possession of Hungary. Reacting in 1529, Suleiman marched through the valley of the Danube and regained control of Buda; in the following autumn, his forces laid siege to Vienna. This was to be the Ottoman Empire's most ambitious expedition and the apogee of its drive to the West. With a reinforced garrison of 16,000 men, the Austrians inflicted the first defeat on Suleiman, sowing the seeds of a bitter Ottoman–Habsburg rivalry that lasted until the 20th century. His second attempt to conquer Vienna failed in 1532, as Ottoman forces were delayed by the siege of Güns and failed to reach Vienna. In both cases, the Ottoman army was plagued by bad weather, forcing them to leave behind essential siege equipment, and was hobbled by overstretched supply lines.