The migration began after al-Muʿizz ibn Bādīs broke with the Fatimid suzerain in 439/1047 and recognized the Abbasid caliph. Because the Fatimids could not easily send an army against the Zirids, the vizier al-Yāzūrī advised directing the nomadic Banū Hilāl and Banū Sulaym from Upper Egypt toward Ifrikiya. The movement promised the tribal chiefs booty and better pastures.

The Arabs began moving west in 442/1050–1 and first ravaged Barqa. The Banū Hilāl continued toward southern Tunisia, while the Banū Sulaym remained in Barqa for several decades before moving onward. Al-Muʿizz initially attempted to use the newcomers as allies, but their raids soon devastated villages and towns. At Haydarān near Gabès in 443/1051–2, the Zirid army was decisively defeated.

The consequences extended beyond immediate warfare. In 449/1057 al-Muʿizz abandoned Kayrawān for al-Mahdiyya, and Kayrawān was sacked. The nomadic groups occupied broad parts of Ifrikiya and the central Maghrib, founding competing principalities and intensifying insecurity. Their arrival also altered the relationship between pastoral and agricultural populations, increasing pastureland at the expense of cultivated fields and contributing to the spread of Arabic rural dialects.

The scale and interpretation of the migration remain debated. Some modern historians have argued that the nomads were less numerous and less destructive than older accounts suggested, and that North African decline had begun before their arrival. Other explanations emphasize catastrophic famine and economic conditions in Egypt under al-Mustansir rather than a purely political Fatimid strategy. Even with these qualifications, the migration marked a major turning point in the social and linguistic history of the Maghrib.