Excerpts from Books and Wikipedia
"Provocative and damaging raids against Christian strongholds in the north had been undertaken during the late 900s by a notorious vizier named al-Mansur, who had become more powerful than the young and feeble caliph whose protector he was supposed to be. But at the turn of the millennium these raids and tauntings of the northern kingdoms were not the cause for the collapse of central caliphal power. Bitter civil wars among the rival Muslim factions of al-Andalus began in earnest in 1009, and for the subsequent two decades they tore apart the “ornament of the world.” Appalled contemporary observers rather poignantly called those self-destructive years the fitna, “the time of strife.” A culture that not long before had been at the peak of its powers was being brought low not so much by barbarians at the gate as by all manner of barbarians within—within its own borders and within the House of Islam. . . . The violent destruction of Madinat al-Zahra, the Versailles of Cordoba, in 1009, just after the beginning of the civil wars, is as good a marker as any of the end of the political well-being of an Islamic polity in medieval Europe."