In Morocco by Edith Wharton — Read

Meanwhile, behind all the Berber turmoil a secret work of religious propaganda was going on. The Arab element had been crushed but not extirpated. The crude idolatrous wealth-loving Berbers apparently dominated, but whenever there was a new uprising or a new invasion it was based on the religious discontent perpetually stirred up by Mahometan agents. The longing for a Mahdi, a Saviour, the craving for purification combined with an opportunity to murder and rob, always gave the Moslem apostle a ready opening; and the downfall of the Merinids was the result of a long series of religious movements to which the European invasion gave an object and a war-cry.

The Saadians were Cherifian Arabs, newcomers from Arabia, to whom the lax Berber paganism was abhorrent. They preached a return to the creed of Mahomet, and proclaimed the Holy War against the hated Portuguese, who had set up fortified posts all along the west coast of Morocco.