 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.