A succession of internal crises—the "Anarchy at Samarra" and the Zanj Revolt—weakened the central government and gave rise to a series of regional dynasties in the provinces of the Abbasid empire.

[4] The weakness of the Abbasid regime allowed the creation of a number of Shi'a regimes in the remoter corners of the Islamic world, such as the Zaydi states in Tabaristan (in 864) and Yemen (in 897),[5] but most notably, it provided the opportunity for the massive spread of the clandestine millennialist Isma'ili missionary movement, which gave birth to the Qarmatians and the Fatimid Caliphate.

This culminated in 945 in the capture of Baghdad by the pro-Shi'a Buyids, who had emerged from humble origins to rule over much of Iran during the previous decade.

[10] The Buyids sponsored Shi'a scholarship, and it was under their patronage that Twelver Shi'ism acquired a definite form both as a sect and as a distinct community, with the elaboration of a specifically Twelver doctrine, and the creation of specifically Shi'a festivals and ritual practices.

[12] During the later 10th century, under the Hamdanid rulers of Aleppo, northern Syria became a major centre of Shi'ism,[13] while the same period saw the emergence of the Alawite and Druze sects.