The Caliphate of Cordoba was a center of architecture and learning in the midst of a backwards and feudal Europe. It was even powerful enough to grab the title of Caliphate in competition with Baghdad after a failed invasion of the Fatmids. Their caliphate was at a golden age in the 10th century, with learning and academia proliferating through Al-Hakam II's library of 40,000 volumes. He also opened up diplomatic relations with the Christian kingdoms of France the Byzantine Empire among others.
Al-Hakam II died peacefully in 976 with Hisham II being his sole heir. The problem with his heir was that he was only 10 years of age, and therefore unfit to rule at the time. Al-Mansur Ibn Abi Aamir, who was his fathers top advisor, took the child under his wing and raised him until adulthood. Over this period of time, he served all of the duties of caliph. As the boy became a man, and as it grew time for him to claim the title of caliph, he began to crave keeping his power more and more. He made Hisham more and more isolated from his people in Cordoba and encouraged heavy Berber immigration in order increase his support base. By the time Hisham was around 20 years of age, he was Caliph in name only, and Al-Mansur Ibn Abi Aamir was Caliph in all but name. By the time of his death in 1008 his son Abd al-Malik and then his brother Abd al-Rahman held the power. Hisham II, being plenty mature enough to rule, grew increasingly discontent with not being able to hold the power of Caliph. When he heard that Abd al-Rahman was going to be present at a raid into Christian territory, he knew that it would be now or never if he wanted to make a powerful move to assert himself.
The night of July 13, 1008, Hisham took around three dozen men loyal to him and armed them. He stormed the palace in a manner that was full of fanfare and also bloodless. He sat in his father's chair and claimed the title of true Caliph, and he invested all power to rule in himself and none in his former advisors descendants. Abd al-Malik, who was present with the advisors, was the only one to speak out against this. He said that he had no place to wield the real power. Hisham II reacted by imprisoning him. The rest of his advisors were spared the fate, and he let them to continue to hold their current position. However, he forcibly weaned himself from their advice to make himself and the title of Caliph steer away from becoming symbolic or ceremonial.
Another act of Hisham II was also performed that night at the raid in León. He sent an assasin to the raid scene to kill Al-Mansur Ibn Abi's brother Abd al-Rahman in order to eliminate a power hungry potential claimant and also to enact some revenge on a personal level. The assasin was successful, with an arrow piercing clean through his heart. The raid party was convinced the killer was Leónese, which made many of them to make a full ransack of the area. The village was devastated, and the raid party came home with a number of items of value. They also found the balance of power shifted.
Hisham II was pleased to see the raid successful, but played on their emotions and acted woeful over Abd al-Rahman's death. One of the men in the group described how he was the only one to have been killed in the raid, and how his killer came out of the dark. He thought that that was very suspicious, and that León must have spies if they knew when the raid was and who was pulling the strings. Hisham took the opportunity to look through the court and his adivsors to eliminate competitors who wanted him out of power and the old system back in place.
By asserting his power, Hisham II was able to keep the title Caliph from degredation to symbol, and he also created some pseudo causus belli to go to war on León, the supposed killer of the man who held power in Cordoba. He wanted to show the Muslim community and the Christian kingdoms that his rule would not falter and that al-Andalus was not destined to fall into the trap of petty, squabbling kingdoms.
I got distracted by some of my other thoughts and ideas while writing my other TL, and this is what came out. The POD, or point of divergence, is that Hisham II grows increasingly discontent with not having power and decides to take action, which he does not in out history. This caused the caliph to become symbolical and caused the collapse of the Caliphate into taifa kingdoms.