 Ferdinand invaded Hungary, but the regent, Frater George Martinuzzi, Bishop of Várad, called on the Ottomans for protection.Suleiman marched into Hungary (see Siege of Buda (1541)) and not only drove Ferdinand out of central Hungary, he forced Ferdinand to agree to pay tribute for his lands in western Hungary.John II Sigismund was also supported by King Sigismund I of Poland, his mother's father, but in 1543 Sigismund made a treaty with the Habsburgs and Poland became neutral.