Answer :
It fell because the divisions within the empire made it vulnerable to attack.
Answer:
The correct answer to the question: According to this source, why did Muslim al-Andalus fall? would be: because the divisions within the empire made it vulnerable to attack.
Explanation:
The reason for this being the correct answer comes from the excerpt itself from the History of the Mohammedan Dynasties in Spain, written by Ibn Said. The excerpt specifically states that after a good time of the land of Andalus being under the control of the Muslim, and seeing years of prosperity, civil war broke out among the inhabitants, and discord settled, to the point that the lands controlled by the Muslim became vulnerable to the Christian kingdoms that now surrouded them and which were reducing the size of their land as they formed alliances to defeat the Muslim. This is why the answer is the one given above.