During the caliphate of ʿAbd al-Malik ibn Marwān (ruled 685–705), which followed the end of the second fitnah, and under his successors during the next four decades, the problematic consequences of the conquests became much more visible. Like their Byzantine and late Sāsānian predecessors, the Marwānid caliphs nominally ruled the various religious communities but allowed the communities’ own appointed or elected officials to administer most internal affairs. Yet now the right of religious communities to live in this fashion was justified by the Qurʾān and the Sunnah; as peoples with revealed books (ahl al-kitāb), they deserved protection (dhimmah) in return for a payment. The Arabs also formed a single religious community whose right to rule over the non-Arab protected communities the Marwānids sought to maintain.

To signify this supremacy, as well as his co-optation of previous legitimacy, ʿAbd al-Malik ordered the construction of the monumental Dome of the Rock in Jerusalem, a major centre of non-Muslim population. The site chosen was sacred to Jews and Christians because of its associations with biblical history; it later gained added meaning for Muslims, who believed it to be the starting point for Muhammad’s miʿrāj (midnight journey to heaven). Although the Dome of the Rock (whose original function remains unclear) and many early mosques resembled contemporary Christian churches, gradually an Islamic aesthetic emerged: a dome on a geometrical base, accompanied by a minaret from which to deliver the call to prayer; and an emphasis on surface decoration that combined arabesque and geometrical design with calligraphic representations of God’s Word. ʿAbd al-Malik took other steps to mark the distinctiveness of Islamic rule: for example, he encouraged the use of Arabic as the language of government and had Islamized coins minted to replace the Byzantine and Sāsānian-style coinage that had continued to be used since the conquests. During the Marwānid period the Muslim community was further consolidated by the regularization of the public cult and the crystallization of a set of five minimal duties (sometimes called pillars).

Yet the Marwānids also depended heavily on the help of non-Arab administrative personnel (kuttāb, singular kātib) and on administrative practices (e.g., a set of government bureaus) inherited from Byzantine and, in particular, late Sāsānian practice. Pre-Islamic writings on governance translated into Arabic, especially from Middle Persian, influenced caliphal style. The governing structure at Damascus and in the provinces began to resemble pre-Islamic monarchy, and thus appealed to a majority of subjects, whose heritage extolled the absolute authority of a divinely sanctioned ruler. Much of the inspiration for this development came from ʿAbd al-Malik’s administrator in the eastern territories, al-Ḥajjāj ibn Yūsuf al-Thaqafī, who was himself an admirer of Sāsānian practice.

The Marwānid caliphs, as rulers of Muslims and non-Muslims alike, had thus been forced to respond to a variety of expectations. Ironically, it was their defense of the importance and distinctiveness of the Arabic language and the Islamic community, not their responsiveness to non-Muslim preferences, that prepared the way for the gradual incorporation of most of the subject population into the ummah. As the conquests slowed and the isolation of the fighters (muqātilah) became less necessary, it became more and more difficult to keep Arabs garrisoned. The sedentarization of Arabs that had begun in the Hejaz was being repeated and extended outside the peninsula. As the tribal links that had so dominated Umayyad politics began to break down, the meaningfulness of tying non-Arab converts to Arab tribes as clients was diluted; moreover, the number of non-Muslims who wished to join the ummah was already becoming too large for this process to work effectively.

Simultaneously, the growing prestige and elaboration of things Arabic and Islamic made them more attractive to non-Arab Muslims and to non-Muslims alike. The more the Muslim rulers succeeded, the more prestige their customs, norms, and habits acquired. Heirs to the considerable agricultural and commercial resources of the Nile-to-Oxus region, they increased its prosperity and widened its horizons by extending its control far to the east and west. Arabic, which occasionally had been used for administrative purposes in earlier empires, now became a valuable lingua franca. As Muslims continued to adapt to rapidly changing circumstances, they needed Arabic to reflect upon and elaborate what they had inherited from the Hejaz. Because the Qurʾān, translation of which was prohibited, was written in a form of Arabic that quickly became archaic to Muslims living in the garrisons and because it contained references to life in Arabia before and during Muhammad’s time, full understanding of the text required special effort. Scholars began to study the religion and poetry of the jāhiliyyah, the times of ignorance before God’s revelation to Muhammad. Philologians soon emerged, in the Hejaz as well as in the garrisons. Many Muslims cultivated reports, which came to be known as Hadith, of what Muhammad had said and done, in order to develop a clearer and fuller picture of his Sunnah. These materials were sometimes gathered into accounts of his campaigns, called maghāzī. The emulation of Muhammad’s Sunnah was a major factor in the development of recognizably “Muslim” styles of personal piety and public decision making. As differences in the garrisons needed to be settled according to “Islamic” principles, the caliphs appointed arbitrating judges, qāḍīs, who were knowledgeable in the Qurʾān and the Sunnah. The pursuit of legal knowledge, fiqh, was taken up in many locales and informed by local pre-Islamic custom and Islamic resources. These special forms of knowledge began to be known as ʿulūm (singular ʿilm) and the persons who pursued them as ulama (ʿulamāʾ, singular ʿālim), a role that provided new sources of prestige and influence, especially for recent converts or sons of converts.

Muslims outside Arabia were also affected by interacting with members of the religious communities over which they ruled. When protected non-Muslims converted, they brought new expectations and habits with them; Islamic eschatology is one area that reflects such enrichment. Unconverted protected groups (dhimmīs) were equally influential. Expressions of Islamic identity often had to take into account the critique of non-Muslims, just as the various non-Muslim traditions were affected by contact with Muslims. This interaction had special consequences in the areas of prophethood and revelation, where major shifts and accommodations occurred among Jews, Christians, Mazdeans, and Muslims during the first two centuries of their coexistence. Muslims attempted to establish Muhammad’s legitimacy as an heir to Jewish and Christian prophethood, while non-Muslims tried to distinguish their prophets and scriptures from Muhammad and the Qurʾān. Within the emergent Islamicate civilization, the separate religious communities continued to go their own way, but the influence of Muslim rule and the intervention of the caliphs in their internal affairs could not help but affect them. The Babylonian Talmud, completed during these years, bears traces of early interaction among communities. In Iraq caliphal policy helped promote the Jewish gaons (local rabbinic authorities) over the exilarch (a central secular leader). Mazdeans turned to the Nestorian Church to avoid Islam, or reconceptualized Zoroaster as a prophet sent to a community with a Book. With the dhimmī system (the system of protecting non-Muslims for payment), Muslim rulers formalized and probably intensified pre-Islamic tendencies toward religious communalization. Furthermore, the greater formality of the new system could protect the subject communities from each other as well as from the dominant minority. So “converting” to Islam, at least in the Nile-to-Oxus region, meant joining one recognizably distinct social entity and leaving another. One of the most significant aspects of many Muslim societies was the inseparability of “religious” affiliation and group membership, a phenomenon that has translated poorly into the social structures of modern Muslim nations. In the central caliphal lands of the early 8th century, membership in the Muslim community offered the best chance for social and physical mobility, regardless of a certain degree of discrimination against non-Arabs. Among many astounding examples of this mobility is the fact that several of the early governors and independent dynasts of Egypt and the Maghrib were grandsons of men born in Central Asia.

The Marwānid Maghrib illustrates a kind of conversion more like that of the peninsular Arabs. After the defeat of initial Amazigh resistance movements, the Arab conquerors of the Maghrib quickly incorporated the Amazigh tribes en masse into the Muslim community, turning them immediately to further conquests. In 710 an Arab-Amazigh army set out for the Iberian Peninsula under the leadership of Ṭāriq ibn Ziyād (the name Gibraltar is derived from Jabal Ṭāriq, or “Mountain of Ṭāriq”). They defeated King Roderick in 711; raided into and through the Iberian Peninsula, which they called al-Andalūs; and ruled in the name of the Umayyad caliph. The Andalusian Muslims never had serious goals across the Pyrenees. In 732 Charles Martel encountered not a Muslim army but a summer raiding party; despite his “victory” over that party, Muslims continued their seasonal raiding along the southern French coast for many years. Muslim Andalusia is particularly interesting because there the pressure for large-scale conversion that was coming to plague the Umayyads in Syria, Iraq, and Iran never developed. Muslims may never have become a majority throughout their 700-year Andalusian presence. Non-Muslims entered into the Muslim realm as Mozarabs, Christians who had adopted the language and manners, rather than the faith, of the Arabs. Given essentially the same administrative arrangements, the Iberian Christian population was later restored to dominance while the Syrian Christian population was drastically reduced, but the Iberian Jewish population all but disappeared while the Nile-to-Oxus Jewish population survived.

The Imazighen who remained in the Maghrib illustrate the mobility of ideologies and institutions from the central lands to more recently conquered territories. No sooner had they given up anti-Muslim resistance and joined the Muslim community than they rebelled again, but this time an Islamic identity, Kharijism, provided the justification. Kharijite ideas had been carried to the Maghrib by refugees from the numerous revolts against the Marwānids. Kharijite egalitarianism suited the economic and social grievances of the Imazighen as non-Arab Muslims under Arab rule. The revolts outlasted the Marwānids; they resulted in the first independent Maghribi dynasty, the Rustamid, founded by Muslims of Persian descent. The direct influence of the revolts was felt as late as the 10th century and survives among small communities in Tunisia and Algeria.