From the Arabian Peninsula, they first migrated to the south of Egypt before heading to the central North Africa. Abu Zayd al-Hilali led between 150,000 and 300,000 Arabs into central North Africa, who assimilated and intermarried with the indigenous peoples. The Fatimids used the tribe, which began their journey as allies and vassals, to punish the particularly difficult to control Zirids after the conquest of Egypt and the founding of Cairo. As the dynasty became increasingly independent and abandoned Shia Islam, they quickly defeated the Zirids and deeply weakened the neighboring Hammadid dynasty and the Zenata. Their influx was a major factor in the linguistic, cultural Arabization of the Maghreb and in the spread of nomadism in areas where agriculture had previously been dominant. Ibn Khaldun noted that the lands ravaged by Banu Hilal invaders had become completely arid desert.