Vlad the Impaler who with Ottoman help had become the Ottoman vassal ruler of Wallachia, refused to pay tribute after some years and invaded Ottoman territory in northern Bulgaria. At that point Mehmed, with the main Ottoman army, was on the Trebizond campaign in Asia. When Mehmed returned from his Trebizond campaign he led a campaign against Wallachia. Vlad fled after some resistance to Hungary. Mehmed first made Wallachia an Ottoman eyalet but then appointed Vlad's brother Radu as a vassal ruler.