Baha ' al - Dawla Baha ' al - Dawla ( died December 22 , 1012 ) was the Buyid amir of Iraq ( 988 – 1012 ) , along with Fars and Kerman ( 998 – 1012 ) . His early reign was dominated by struggles with his rival relatives over control of the western Persian provinces , but by 998 he managed to establish his supremacy over the Buyid confederation . His reign nevertheless saw the increasing encroachment of neighbouring powers on Buyid territory , and marks the beginning of the decline of the Buyids ' power . Biography . He was the third son of ' Adud al - Dawla . Upon the death of his brother Sharaf al - Dawla in 988 , Baha ' al - Dawla succeeded him , whereupon he took the additional title of " Diya ' al - Milla " . Another brother , Samsam al - Dawla , prevented Baha ' al - Dawla from gaining all of Sharaf al - Dawla ' s possessions by taking control of Fars , Kerman and Khuzestan . Both Baha ' al - Dawla and his brother , however , were threatened by their granduncle Fakhr al - Dawla , the ruler of Jibal , who invaded Khuzestan in an attempt to drive a wedge between the two brothers ' territories . This act prompted the brothers to draw up an alliance . Samsam al - Dawla recognized Baha ' al - Dawla as the ruler of Iraq and Khuzestan , while he himself kept Arrajan , Fars and Kerman . Both promised to consider each other as equals , and took the title of king ( " malik " ) . In 991 Baha ' al - Dawla attempted to gain supremacy over Samsam al - Dawla ' s realm . He took the ancient Persian title of " Shâhanshâh " and invaded the latter ' s territory . His forces were defeated , however , and Samsam al - Dawla regained Khuzestan and even gained control of the Buyid territories in Oman . He then recognized Fakhr al - Dawla as senior " amir " , submitting to his authority . Fakhr al - Dawla ' s death in 997 , coupled with Samsam al - Dawla ' s increasing troubles within his realm , provided Baha ' al - Dawla with the opportunity to assert his authority in Persia . He gained the support of the Kurdish ruler Badr ibn Hasanwaih and prepared for the expedition . The invasion began in December 998 ; scarcely had it commenced when Samsam al - Dawla was killed by one of the sons of ' Izz al - Dawla who had risen in revolt . Baha ' al - Dawla then took Shiraz and defeated ' Izz al - Dawla ' s sons . For the rest of his life Baha ' al - Dawla remained in Fars . He also managed to gain indirect control over northern Iran , where Fakr al - Dawla ' s two sons Majd al - Dawla and Shams al - Dawla recognized him as senior " amir " by 1009 or 1010 . Baha ' al - Dawla ' s reign coincided with the beginning of the decline of the Buyids . The Kurdish chief Badh laid the foundations for the Marwanid amirate in Diyarbakr , while the initially subservient ' Uqaylids of Mosul expanded into Iraq at the Buyids ' expense . By the time Baha ' al - Dawla died , Baghdad and Wasit were the only two major Iraqi cities directly under his control . In the north , where Fakhr al - Dawla ' s sons ruled , the Buyid frontier also fell back , as the Ziyarids of Gorgan and Tabaristan permanently wrested themselves from Buyid control . The Ghaznavids kept putting pressure on the Khurasan border , while the Kakuyids began to set up a state in Isfahan . For various reasons , Baha ' al - Dawla did not actively defend the borders . Having gained undisputed control of the Buyid state , he seemed content to allow external enemies to seize territories in the west and north . He died in Arrajan in December of 1012 . Shortly before his death , he named his son Sultan al - Dawla as his successor .