 Seizing upon their absence, Ferdinand I attempted to enforce his claim as King of Hungary.In 1527 he drove back the Ottoman vassal John Zápolya and captured Buda, Győr, Komárom, Esztergom, and Székesfehérvár by 1528.Meanwhile, the Ottoman Sultan, Suleiman the Magnificent, took no action at this stage despite the pleas of his vassal.