When Muslims conquer, it's described without adjectives. When Christians conquer, it's bloody, cruel, etc. Typical modern and inaccurate historiography. The First Crusade is launched just like that, with no apparent reason. To explain it, Clark would have to admit that the Muslim Turks have conquered Asia Minor and the Eastern Empire was about to fall. The First Crusade gave 400 more years to the Eastern Empire.
Review of The Story of Europe
