"andalus (the iberian peninsula), which was conquered in the year 92 of the hijra, continued for many years to be a dependency of the eastern khalifate, until it was snatched away from their hands by one of the surviving members of the family of umeyyah (umayyad), who, crossing over from barbary, subdued the country, and formed therein an independent kingdom, which he transmitted to his posterity. during three centuries and a half, andalus, governed by the princes of this dynasty, reached the utmost degree of power and prosperity, until civil war breaking out among its inhabitants, the muslims, weakened by internal discord, became every where the prey of the artful christians, and the territory of islam was considerably reduced, so much so that at the present moment the worshippers of the crucified hold the greatest part of andalus in their hands, and their country is divided into various powerful kingdoms, whose rulers assist each other whenever the muslims attack their territories." 悠bn said, book of the maghrib, in ahmed ibm mohammed al-makkari, the history of the mohammedan dynasties in spain, translated by pascuual de gayangos s, (london: oriental translation fund, 1840), 1, 95-102 according to this source, why did muslim al-andalus fall?