The Muslims who remained in Spain were promised religious tolerance, but in the early 1500s, were all forced to convert to Christianity, and became known as Moriscos. The Moriscos continued to speak the Arabic language (or the Berber language of North Africa) and to wear Moorish dress.
Despite their public conversion, the Moriscos were distrusted by the "Old Christian" population from northern Spain, who considered them insincere converts and secret Muslims. In fact many continued to practice Islam in secret. The Moriscos suffered increasing intolerance and persecution in the Spanish Inquisition.
In the mid-16th century, Ottoman Turkey emerged as the dominant Muslim power in the Mediterranean Sea. There were increasing clashes between Turkey and Castile. Philip II of Spain feared that the Moriscos of Granada might aid a potential Turkish invasion of Spain. The Ottoman court planned an armed intervention in favor of the Moriscos, but the Ottoman Sultan, Selim the Grim, was influenced to invade Cyprus instead because of its vinyards.
In 1567, Philip II issued a royal decree ending all toleration of "Moorish" ways. He banned the speaking of Arabic or Berber, banned Moorish dress, required Moriscos to adopt Christian names, and ordered the destruction of all books and documents in Arabic script. Morisco children would be educated exclusively by Catholic priests. This decree broke earlier pledges of toleration.
It is alleged that Philip issued this decree with the intent of provoking rebellion, so the Moriscos could be destroyed or expelled. This may be true, or Philip may have wanted to ensure the loyalty of the Moriscos by complete assimilation.
On Christmas Eve 1568, representatives of the Moriscos of Granada, the Alpujarras, and elsewhere clandestinely assembled at the Vale de Lecrin. They acclaimed Fernando de Valor as their king, under the name Aben Humeya, and repudiated Christianity.
The insurrection was led by Aben Humeya, and took the form of guerrilla warfare against the Castilian forces in the Alpujarras.