Mehmed I was succeeded by his son Murad II (1421-51) which is seen as a time of preparation for the extension of empire under Mehmed II ‘Fatih’, ‘the Conqueror’. The first few years of his reign were engaged in struggles to ensure the unity of state, such as the revolt of his uncle ‘Düzme’, ‘the Impostor’, Mustafa who had Byzantine support. Murad was essentially a peace-loving Sultan and once he thought he had made peace on all sides, he voluntarily renounced the throne in favour of his son Mehmed II (summer 1444, when Mehmed was only 12 years old) but he was petitioned to come back and command the Ottoman army against a new Hungarian-Byzantine offensive. He won a victory at Varna, and returned to the throne until his death in 1451 (Mehmed was now 19).