 Before the eleventh century, most of North-West Africa was a Berber-speaking Muslim area.The process of Arabization only became a major factor with the arrival of the Banu Hilal, a tribe sent by the Fatimids of Egypt to punish the Berber Zirid dynasty for having abandoned Shiism.The Banu Hilal reduced the Zirids to a few coastal towns and took over much of the plains; their influx was a major factor in the Arabization of the region and in the spread of nomadism in areas where agriculture had previously been dominant.