Islam, however, was destined for a world role. Under Muhammad’s successors the expansionist urge of the tribes, temporarily united around the nucleus of the two sacred enclaves, coincided with the weakness of Byzantium and Sāsānian Persia. Tribes summoned to the banners of Islam launched a career of conquest that promised to satisfy the mandate of their new faith as well as the desire for booty and lands. With families and flocks, they left the peninsula. Population movements of such magnitude affected all of Arabia; in Hadhramaut they possibly caused neglect of irrigation works, resulting in erosion of fertile lands. In Oman, too, when Arab tribes evicted the Persian ruling class, its complex irrigation system seems to have suffered severely. Many Omani Arabs about the mid-7th century left for Basra (in Iraq) and formed the influential Azd group there. Arabian Islam replaced Persian influence in the Bahrain district and Al-Ḥasā province in the northeast, and in Yemen.
As the conquests far beyond Arabia poured loot into the Holy Cities (Mecca and Medina), they became wealthy centres of a sophisticated Arabian culture; Medina became a centre for Qurʾānic study, the evolution of Islamic law, and historical record. Under the caliphs—Muhammad’s successors—Islam began to assume its characteristic shape; paradoxically, outside the cities it made little difference to Arabian life for centuries. Sharīʿah (Islamic law), promoted often by the Prophet’s own descendants, developed in the urban centres; but outside them customary law persisted, sometimes diametrically opposed to Sharīʿah. In time the Hejaz and Yemen came to make notable contributions to Islamic culture, but Islam’s basically Arabian nature first shows in the early mosque, which resembles the pre-Islamic temple, and in the pilgrimage rites, little altered from paganism. Struggle for leadership
In Arabia offices were generally hereditary and elective, but on Muhammad’s death Abū Bakr, the first caliph, aided by his own eventual successor, ʿUmar, gained the leadership that Quraysh might have lost to others. They were not of the house of Hāshim, which, from the outset, felt cheated of its rights. ʿAlī, Muhammad’s stepbrother and son-in-law, became the focus of legitimist claims to succeed the Prophet. ʿUthmān, however, the third caliph, was descended from both the Umayyah and Hāshim branches of ʿAbd Manāf. The latter half of ʿUthmān’s reign coincided with a slackening in the tide of conquest. ʿUthmān was censured for diverting property, revenues, and booty in Iraq and Egypt to his Quraysh relatives. Squabbles with the tribes resulted in ʿUthmān’s murder at Medina by opponents from Egypt. ʿAlī was proclaimed caliph by the anṣār, but he lost the political battle with ʿUthmān’s powerful relative Muʿāwiyah, governor of Syria, who demanded retaliation against the murderers. ʿAlī was later murdered by a Khārijite, a member of a dissident group. ʿAlī had quitted Medina for Iraq, and the political power centre of Islam left the peninsula, never to return. ʿAlī’s posterity, however, played a key role in subsequent Arabian history. The Umayyad and ʿAbbāsid periods Regional centres
Once Muʿāwiyah and the Umayyads had seized overlordship of the far-flung Islamic empire, which they ruled from Damascus, the Holy Cities remained only the spiritual capitals of Islam. The Umayyad caliphs appointed governors over the three crucial areas of the Hejaz, Yemen, and Oman, but in Iraq occasional powerful governors managed to control the Persian Gulf provinces, the gulf being an important maritime trade route, especially under the ʿAbbāsids. Occasionally Bahrain, Al-Ḥasā, and Najd also became regional centres of power within Arabia.
The brief unity that Islam had imposed on the Arabian Peninsula was irrevocably broken as the main Islamic sects took shape—the “orthodox” Sunnis and the “legitimist” Shīʿites (who were distinguished from the Sunnis principally by their tenet that the imam of the Muslim community must be descended from ʿAlī by Muhammad’s daughter Fāṭimah).
Umayyad forces defeated a Quraysh pretender, ʿAbd Allāh ibn al-Zubayr, who had been proclaimed caliph in the Hejaz. Medina was captured; Mecca was besieged, the ḥaram bombarded, and the Kaʿbah set on fire (the sacred Black Stone—an object of veneration probably appropriated from pre-Islamic religion—was split in three places). The harsh Umayyad general al-Ḥajjāj captured the city, and the pretender perished. The violation of the sacred enclaves by troops, including Arab Christians, was an act of sacrilege, but it broke any power remaining with the tribal “supporters” in Medina. The Prophet’s original simple mosque in Medina, already enlarged by the early caliphs, was rebuilt by the Umayyad al-Walīd (it has been much altered and restored since). The Umayyads spent lavishly on the Holy Cities and developed Hejaz irrigation.
The Umayyads collapsed before the ʿAbbāsids in 750, a fall to which rivalry between the tribes, aligned as northern and southern Arabs, contributed materially. The ʿAbbāsids claimed adherence of the Legitimists, since their ancestor, the Prophet’s uncle, was of the Hāshimite house. The ʿAbbāsids maintained a policy of strict adherence to religious observance, and they too devoted large sums to supporting and embellishing the Holy Cities, to which they sent annually a pilgrim caravan. Zubaydah, wife of the caliph Hārūn al-Rashīd, celebrated for her public works, is said to have ordered the construction of the qanāt, a tunneled conduit that took water to Mecca. The threat of insurrection by Legitimist pretenders of the ʿAlīd branch of the Hāshimite house—who denied ʿAbbāsid claims to the caliphate as they had with the Umayyads—was a constant danger to the ʿAbbāsid caliphs. The ʿAlīd family developed both Sunni and Shīʿite branches, but the latter split into a multiplicity of sects, of which the most important are the “Twelvers” (Ithnā ʿAshariyyah, or Imāmīs), who recognized 12 imams, and the Ismāʿīlite “Seveners” (Ismāʿīliyyah, or Ismāʿīlīs, for Imam Ismāʿīl ibn Jaʿfar), who acknowledged only seven. Yemen
To quell a rising in Yemen, the ʿAbbāsid caliph al-Maʾmūn dispatched Ibn Ziyād, who refounded in 820 the southern city of Zabīd and became overlord of Yemen, Najrān, and Hadhramaut. About a century later the Najāḥids—Ethiopian slaves or local Afro-Asians—supplanted the Ziyādids in Zabīd; however, though independent, neither dynasty renounced vague ʿAbbāsid suzerainty. The Banū Yaʿfur, lords north of Sanaa, expelled the Ziyādid governor and ruled independently from 861 to 997. Najāḥid rule ended when ʿAlī ibn Mahdī captured Zabīd in 1159. The Qarmatians
A more serious loss to ʿAbbāsid power in Arabia was occasioned by the appearance of Ismāʿīlite propaganda in Yemen about 880, in eastern Arabia about 899, and even briefly in Oman. From Yemen, Ismāʿīlīs reached North Africa, where the Fāṭimid movement arose and conquered Egypt and for a time seriously threatened the ʿAbbāsids in Baghdad. The Qarmatians (Qarāmiṭah), an extremist offshoot of the Ismāʿīlīs, founded a state in Al-Ḥasā, in northeastern Arabia. They set out to subvert Sunni Islam. They were alleged to oppose many of the teachings of the Prophet Muhammad, and they encouraged social equality for nomads, townspeople, and peasants. In 930 the Persian Gulf Qarmatians plundered Mecca, carrying off the Black Stone to Al-Ḥasā; they later returned it under Fāṭimid pressure. The Qarmatians were overthrown in 1077–78 by local Sunni tribes, but Qarmatian influence persisted in Bahrain. From the 13th century, Twelver, or Imāmī, Shīʿism spread in Al-Ḥasā and Bahrain, while political power was held by the Shīʿite Sevener Jarwānid dynasty (1305 to about 1450).