In 1446 Murad II returned to throne, Mehmed II retained the title of sultan but only acted as a governor of Manisa. Following death of Murad II in 1451, Mehmed II became sultan for second time. İbrahim Bey of Karaman invaded disputed area and instigated various revolts against Ottoman rule. Mehmed II conducted first campaign against İbrahim of Karaman; Byzantines threatened to release Ottoman claimant Orhan.