The Christian kings of Castile and León had meanwhile profited by the wars of the _taifa_ states to make conquests or to reduce many of the _taifas_ to the payment of tribute. Even Seville was tributary to a Christian king. This inclined many of the Moslem princes, realizing their own helplessness, to invite a newly-risen Mohammedan power in northwestern Africa to come to their aid. The rulers of the _taifas_ recognized that their own authority might be endangered by the entry of their coreligionists, but their feelings were well expressed in the words attributed to the ruler of Seville: “I would rather be a camel-driver in Africa than a swineherd in Castile.” The African people referred to were a branch of the Berbers who had dwelt apart in the Sahara Desert. Converted at length to the Moslem faith, they became fanatically religious, taking to themselves the name “Almoravides” (religious men), and launching themselves forth to the conquest of all northwestern Africa. The African empire of the Almoravides was already an accomplished fact when their emperor, Yusuf, was invited to help the Spanish Moslems under a promise that he would not deprive the _taifa_ rulers of their states. In 1086 Yusuf entered Spain, and encountered the army of Alfonso VI of León at Zalaca, near Badajoz. Yusuf was completely successful, and the Christian peril was rolled back, but no counter-conquests of moment were made. Yusuf himself returned to Africa. Four years later the Moslem princes had need of Yusuf, and once again he came to avert the threatening danger. By this time popular opinion, reinforced by the intrigues of the Moslem priesthood, desired the establishment of Yusuf’s authority in Spain; the restoration of a single rule, it was believed, would check the Christian kings, and bring peace and prosperity. By 1091 Yusuf had reduced all of the _taifa_ princes except the king of Saragossa, and the latter was subjected by Yusuf’s successor. Thus the unity of Moslem Spain was again accomplished.[18] [Sidenote: Rise of the Almohades.] The Almoravide rule rested very lightly on the Moslem population, but only for a short time. The emperors lost their religious enthusiasm, and not only did they fail to advance the conquest but they also gave themselves up to a life of luxury and dissipation. Public security declined, with the result that the people now wished to rid themselves of the sovereigns whom formerly they had desired so much. At this time there came a tremendous uprising in Africa in 1125 of the Moors of the Moroccan Atlas, an uncivilized branch of the Berber family. They had become fanatical Mohammedans, and like their Almoravide predecessors had taken a name springing from their religious faith, that of “Almohades” (unitarians). Uncultivated as they were, they were able to master the military art of that day sufficiently to overwhelm the Almoravide power in Africa, though only after a long war. [Sidenote: The Almohades in Spain.]