Izz al-Dawla continued his father's policy of fighting the Shahinids who ruled the Iraqi marshlands, but he was unable to overcome them. At the same time, he ignored the border with the Byzantine Empire, considering this to be a matter for the caliph to handle. When the Byzantines under John I Tzimisces overran much of northern Mesopotamia in 971, he did not even return to Baghdad. The person who took it upon himself to defend Iraq was Sebük-Tegin, who felt himself increasingly alienated from the Buyid. Two years later, Izz al-Dawla appointed Ibn Baqiyya as his "vizier".