The Arabs and western troops from Baghdad, displeased at the choice, attacked the assembly, broke open the prison, and plundered the armory. They were attacked by the Turkish and Berber soldiers, and after a round fight, in which many fell, succumbed. Baghdad had yet to learn that the Caliphate no longer depended on Arabian choice, but had passed into other hands.
The governor of Baghdad persuaded the city to submit, and the succession was thereafter acknowledged throughout the land. Al-Mu'tazz and his brother, threatened by the troops, resigned their title to succeed, and were then, by way of protection, kept in confinement. On a second outbreak in their favor, the Turks would have put them both to death, but the Vazir interposed and saved their lives, for which act of mercy, his property was seized by the Turkish soldiers, and himself banished to Crete. The Empire, in fact, both at home and abroad, had passed into the hands of Turks.
In 863, the Muslim campaign against the Christians was singularly unfortunate. Two whole corps in Armenia and Asia Minor, some 3,000 strong, with their leaders, were killed. The tidings drove Baghdad wild. The ancient cry for a Holy War rang through the streets. People blamed the Turks that had brought disaster on the faith, murdered their Caliphs, and set up others at their pleasure.
With such cries the city rose in uproar; the prisons were broken and the bridges burned. But Baghdad could no longer dictate to its rulers; it could only riot. The crusading spirit was, however, strong enough to draw men from the provinces around, who flocked as free lances to fight against the infidel. But the Turks cared for none of these things, nor did the Caliph.
In 865, the end for al-Musta'in himself was now at hand. After some disagreements between Turkish leaders that brought danger to al-Musta'in, he, along with two other Turkish leaders, left Samarra on a boat to East Baghdad. The Turks sent after him a party of their captains, requesting him to return to Samarra. But the Caliph refused, and hard words followed between the two sides, in the heat of which one of the Turkish speakers received a blow.
The insult rankled in their minds, and on returning to Samarra, the troops rose jointly, and bringing forth al-Mu'tazz from his confinement, saluted him as Caliph. Within a few weeks, his brother Abu Ahmed, with 50,000 Turks and 2,000 Berbers, besiege Baghdad throughout the year 865.
Beginning of 866, driven to extremities by plots and treachery all around, induced al-Musta'in by alternate threats and promises to abdicate in favor of al-Mu'tazz. He was to live at Medina with a sufficient income; the conditions signed, the Governor received the ministers and courtiers of al-Musta'in, and having assured them he had done what he had for the best and to stop further bloodshed, sent them to Samarra to do homage to the new Caliph, who ratified the terms, and took possession of Baghdad in the early days of 252 AH (866 AD). He also sent to al-Musta'in his mother and family from Samarra, but not until they had been stripped of everything they possessed.
Instead of finding a refuge at Medina, al-Musta'in found himself kept in Baghdad. There he was put to death by the order of al-Mu'tazz. Carrying al-Musta'in's head to the Caliph, "Here," cried the executioner, "behold thy cousin's head!" "Lay it aside," answered the heartless al-Mu'tazz who was playing chess,—"till I have finished the game." And then, having satisfied himself that it was really al-Musta'in's head, he commanded 500 pieces to be given to the assassin as his reward.