The Expansion of Islam from Mecca, Medina and the Hijaz region began with the Prophet Muhammad's death in 632. This had been prefigured by his letter to Emperor Heraclius inviting him to accept submission to God--Islam. At Muhammad's death tribes newly joined to his polity tried to break away, and the subsequent punitive expeditions--Ridda Wars--phased into the dramatic conquests of all of the Sassanian and much of the Byzantine lands. By 635, Damascus and Homs were in Muslim Arab hands, and after the resounding defeat of Byzantine forces at the Battle of the Yarmuk (636), Palestine and the rest of Syria were open to Islam. Jerusalem and Antioch were taken in 638, at which point Islamic armies began both westward and eastward offensives. By the 650s, Egypt was taken, as was North Africa to Cyrenica, where Berbers resisted fiercely at first, later converting to Islam, allowing the subjugation of Tunisia and Carthage by 695. In the East, after the momentous Battle of Qadisiyya on the Euphrates in 637, Ctesiphon fell, as did Mosul in 641. A further Sassanian defeat at Nahavand in 642 opened up the entire Iranian plateau. Qazvin and Ray near Tehran were taken in 643. Persepolis was conquered in 650, and Arab Muslim armies had reached Merv on the Oxus River by 651. In the next thirty years, Arab Muslim raids would course throughout Byzantine Anatolia, ravaging regions in Cappadocia, as well as Nicaea in western Asia Minor on a regular basis. In 687 Arab armies laid siege to Constantinople for the first time, in aspired-to fulfillment of Prophetic dicta.
Spain had been under Visigoth control since the middle of the fifth century. At first, they were not well received by the local population, being Arian as opposed to the majority's Catholicism. Within a century, they had accepted Catholicism and received in return clerical cooperation. Still, political technology was limited, and weak or young-perishing kings had not been able to weld together a coherent state. Also, persecution of the growing Jewish population removed their potential support. Thus, after Arab armies had consolidated their hold on North Africa and begun converting the interior's Berbers to Islam, the Arab-Turkish Muslim Amir (commander) Tariq, crossed over to Gibraltar (Jabal-Tariq, the mountain of Tariq), and launched a nine-year conquest of Iberia up to the Pyrenees (711-20), annihilating the Visigothic state. Provence and Aquitane were now raided frequently. During the same years, on Islam's northeastern borders, adventurous Amirs conquered Transoxiana, beyond the Oxus River, and the Oxus delta by 715, while in the south, Sind, in present-day Pakistan, was taken by 713. Back in the European sphere, only Charles Martel's defeat of Muslim forces in the Battle of Tours near Poitiers in 732, combined with Leo III's defeat of Muslim besiegers at Constantinople in 717, halted the new religious polity's advances, until ninth century forays into the Mediterranean.
In addition to these advances in the foreign realm were changes in the Islamic polity's--Dar al-Islam--internal make-up. Upon Muhammad's death, immediately a crisis emerged related to who should rule the new political-religious unit. He had gathered around him in fifteen or so years of preaching close colleagues. Many of them were acquired in Mecca. One of the closest was Ali, a cousin. As well, there were supporters who had come to the banner later, in Medina. While Muhammad was being prepared for burial by Ali, Meccan companions--the muhajirun, those who had migrated with the Prophet to Medina--were entangled in succession debate with Medians--ansar, or those who assisted the muhajirun on their arrival in Medina. In order to prevent further strife, Umar, a prominent member of Muhammad's own tribe and an early convert, convinced his colleague and kinsman Abu Bakr to become leader of the Muslims. His title was khalifa (Eng. Caliph), or successor to Muhammad, the Messenger of God. Whereas the majority of ansar and muhajirun accepted his candidacy, an undercurrent of opposition continued, claiming that Ali was entitled, being close to Muhammad, pious, and perhaps even nominated by the Prophet as his successor. Umar (r. 634-44) succeeded him, and presided over the first wave of conquests. This brought large numbers of non-Muslims under their control. Those Christians and Jews among them were dubbed people of the book and were allowed to practices their religions freely, though were made to pay a special tax called the jizya. To this protected category were later added Zoroastrians, a sign of Islamic pragmatism. As well, great numbers of non-Arabs converted to Islam, and were called mawali, or clients of the original Arab conquerors.
Along with continuing sentiment in favor of Ali, dissension began to permeate the Islamic state during the tenure of Caiph Uthman (644-656). He was a member of the leading branch of the Quraysh tribe in Mecca, the branch that had actively opposed Muhammad's mission prior to 632. He reasserted the tribal aristocratic prerogatives, appointing family-members to nearly every possible position, among them Muawiya as governor of Syria. When Uthman was assassinated by soldiers from Egypt, some members of the Ummayad branch suspected the new Caliph Ali as the chief conspirator. Muawiya became the standard-bearer of this group, openly rebelling against the Iraq-based Ali by 658 as an anti-Caliph. They eventually met in battle, and though Ali's forces were prevailing, he agreed to arbitration. The arbitrators were disposed towards Muawiya, so the proceedings did not go well for Ali. By 661, on Ali's death, Muawiya was able to establish himself as Caliph, founding the hereditary Ummayad dynasty of Caliphs centered in Damascus. It was he and his descendents that directed the next phase of conquest and laid siege to Constantinople. However, from this time forwards, permanent political rifts developed in the Islamic world, now called umma or super-tribe. A group called 'Partisans of Ali' evolve into the Shi'ite form of Islam (Shia: Party or Faction). They believed that only Ali had had legitimate rights of succession to Muhammad. Further, only Ali's descendants were entitled to be Caliph. This premise, as well as early Ummayad massacre of Ali's son and successor Husayn and his supporters at Karbala in 686, caused them to view all Islamic political leaders except Muhammad and Ali as illegitimate. The exception were the Imams, or direct descendants of Ali, the twelfth of which went into occultation, or temporary disappearance, in 987.
The Ummayad dynasty lasted until 751. It was the particularly Arab period of Islam. Arabs were accorded precedence in all matters, with new non-Arab uslims, or mawali, being forced into subservient roles. In some cases, taxes akin to jizya were imposed on them. As for non-Muslims, Ummayads did not encourage their conversion, recognizing their financial benefit.
During the 740s, dissension in the Islamic east among non-Arabs mounted, especially in Persia, which possessed a rich civilizational history and resented upstart Arab domination. Certain dissidents in the East, such as Abu Muslim, were able to galvanize generalized support for Ali as well, under the auspices of a new faction from the Quraysh called the Abbasids. By the end of the decade, enfeebled Ummayad Caliphs were not able to put down growing rebellion in Iraq and Persia, such that the Abbasids were able to come to power in 751, claiming to be the upholders of true Islamic piety blind to ethnicity, as well as the cause of Ali, which they jettisoned in the next decades.
Reflecting new geopolitical and ethnic realities in the umma, the Abbasids moved the caliphal capital to Iraq, building Baghdad soon after. It was during the early to mid-Abbasid period (751-830) that the true flowering of Islamic civilization occurred encompassing law, theology, visual arts, and scientific enquiry. Also, while a modus vivendi was worked out with Byzantium involving yearly skirmishes and a mostly fixed border, in the West, an Ummayad Amir named Abd al-Rahman had escaped Abbasid massacre and crossed to Spain, founding the Ummayad Emirate of Spain from 756. This gave Iberian Islam political centralism for a while, though his descendents underwent political fragmentation.
Also at the end of the eighth century the Abbasids found they could no longer keep a huge polity larger than that of Rome together from Baghdad. In 793 the Shi'ite dynasty of Idrisids set up a state from Fez in Morocco, while a family of governors under the Abbasids became increasingly independent until they founded the Aghlabid Emirate from the 830s. By the 860s governors in Egypt set up their own Tulunid Emirate, so named for its founder Ahmad ibn Tulun. From this time Egypt would be ruled by dynasties separate from the Caliph. In the East as well, governors decreased their ties to the center. The Saffarids of Herat and the Samanids of Bukhara had broken away from the 870s, cultivating a much more Persianate culture and statecraft. By this time only the central lands of Mesopotamia were under direct Abbasid control, with Palestine and the Hijaz often managed by the Tulunids. Byzantium, for its part, had begun to push Arab Muslims farther east in Anatolia.
By the 920s, the situation had changed further. A Shi'ite sect only recognizing the first five Imams and tracing its roots to the Prophet's daughter Fatima took control of Idrisi and then Aghlabid domains. Called the Fatimid dynasty, they had advanced to Egypt in 969, establishing their capital near Fustat in Cairo, which they built as a bastion of Shi'ite learning and politics. By 1000 they had become the chief political and ideological challenge to Sunni Islam in the form of the Abbasids. By this time the latter state had fragmented into several governorships that, while recognizing caliphal authority from Baghdad, did mostly as they wanted, fighting with each other. The Caliph himself was under 'protection' of the Buyid Emirs who possessed all of Iraq and western Iran, and were quietly Shi'ite in their sympathies. To the East was the first major Turkish Islamic state, the Ghaznavids under Mahmud.
In the Islamic West, after generations of political infighting among rival Islamic Amirs, the Ummayad Abd al-Rahman III was able to establish himself a Caliph of a united polity. Centered on Cordoba and Toledo, he and his vizir al-Mansur raided both the Shi'ite Fatimids as well as the Christian neighbors at Barcelona, Burgos, Leon, and Santiago de Compostela. As for the Christian states on the peninsula, from the 730s, the tiny Kingdom of Asturias, centered on Oviedo in northern Spain, had soldiered on, exposed to continuous Muslim raiding. This was in addition to Charlemagne's March in Catalonia on the Pyrenees. In the early 900s, the Asturias king took advantage of Muslim infighting to move his capital south to Leon and the County of Castile. Though not a Crusader-type state and content to work with Muslim amirs in order to survive, its leaders began to attract freemen as colonists with generous offers of agricultural land and tax rebates. Warring with Muslims when it suited them, Castilian leaders were not at this point fighting a holy war. For their part, Abd al-Rahman's forces raided Pamplona, but did not prevent slow advances out of the Pyrenees, based on fortress building and conquest of Christian held points. Good relations with al-Mansur were maintained. By 1034, Sancho the Great had incorporated Aragon, Sobrarbe, Barcelona, as well as Asturian Leon and Castile.
The Islamic polity of the 700s, which had encapsulated the majority of the known world of Antiquity in lightning speed, had its roots in pagan Arab tribesmen mired in clannish warfare, and mostly illiterate. The obvious question is how they were able to conquer the Sassanians, route the Byzantines, and establish a state from Spain to India. Before moving to internal issues, let us consider the environment. The two states against which early Islam abutted were Byzantium and Sassanian Persia. As regards the latter, in the 630s, it was in the midst of coups a the political center occasioned by the momentous loss to Byzantium under Heraclius. As well, none of its border defenses had been resurrected since the conflict, and its army size was much reduced. Client tribes in northern Arabia, the Lakhmids, were only nominally loyal, and had used the war years to drift away from Persian control. Thus, the Arabs were facing a northeastern enemy that was much enervated, and not able to attract the emotional loyalty of a mostly non-Zoroastiran population in areas of initial Sassanian-Islamic conflict. Byzantium's condition was not dissimilar. It too had not had time to restore defenses in those areas from with the Persian had withdrawn only recently, such as the Levant and Egypt. It too, had suffered tremendous human and material losses. Further, its client Arabian tribes, the Ghassanids, had also drifted away when not paid. More unique to Byzantium, however, was the religious issue. Though the Levant and Egypt were solidly Christian, its population's majority was not Orthodox. Monophysitism was dominant in Egypt and parts of Palestine, while Nestorianism was widespread in Syria and Mesopotamia. As emperors and the Constantinople church had gone back and forth on the issue, ultimately condemning and proscribing both approaches, Byzantine administration had gone a long way to alienating large segments of the population in those very areas Muslims were to conquer with their offers of religious toleration in return for political control. This was also true for the Jewish communities scattered throughout the region. Thus, there was very little reason for many to defend Byzantium in the Middle East. Finally, one cannot avoid the sense that after forty years of internal political unrest combined with exhausting Persian wars and Avar incursions, Byzantine state, society, and military exhibited a sense of fatigue and inability to assimilate the crisis' meaning so soon after the Sassanian conflict. Of course, the element of chance--a dust storm blinding Byzantine troops near the Yarmuk--cannot be discounted.
Turning to factors internal to the Muslims, the most mundane are nonetheless important. The Islamic umma was something with which tribal Arabs could identify. A super-tribe based on allegiance to a leader who had demonstrated increasing success at beating opponents, the prospect of raiding on a wider scale after 634 would be lucrative and quite attractive to them. Often tribes as a whole came into the new religion, and were deployed and settled as such. Beyond that, Arab fighters, on foot and horseback, were light and mobile, much more so than their Byzantine or Persian counterparts. Not having population centers and always on the move, it was impossible for Byzantine forces in particular to draw them into the kind of combat conducive to victory. In such a situation, raiding success bred enthusiasm for continual conquest, with over-extension not a danger.
All this suggests similarities to the Germanic invaders in Europe, and still more, to the Huns after them. There are, however, important, definitive differences that explain both the success and longevity of the new enterprise. First, Muslims did not come to raid and destroy, but to settle. All of their substantial military initiative resulted in settlement and Islamization--permanently, with the exception of Spain, which remained in their hands for over 700 years. Furthermore, far from having a defective understanding of a civilization which they then proceeded to degrade, as in the case of Germanic invaders, Muslims newly arrived in Byzantine or Persian lands openly embraced existing techniques of administration, and intellectual heritages. Indeed, essential to their program was to leave as much as possible that was not directly offensive to Islam unaffected in conquered areas. This pragmatism--evident in according to Zoroastrianism the 'people of the book' status--was seen everywhere, and appears to have been well thought out. As far as the Germans were concerned, it is almost impossible to locate anything like policy as such, beyond personal enrichment, up to the Carolingian period.
Finally, the new religion itself was integral to political success. By incorporating values consonant with pre-Islamic Arabian tribal culture, Islam was not a civilizational break that would deprive it of early supporters. Such values included martial honor, tolerance for those weaker or defenseless, strong bonds to the family, clan, and tribe--all now defined in religious terms--as well as permission to plunder conquered areas within reason. Further, integration of previous pagan religious practices, now in a cleansed Islamic form, allowed new adherents to assimilate the faith's ideas more easily. Use of the Ka'ba in Mecca as a shrine is a perfect example. The basic creed of Islam, as it existed in the 650s then, was the following: a strict monotheism only paying allegiance to Allah, with Muhammad as his last and most important messenger verifying and improving Judaism and Christianity. It's strictures included 1) profession of faith (there is no god but God and Muhammad is his messenger); 2) prayer five times daily; 3) alms to the poor; 4) fasting during the daytime of the holy month of Ramadan; and 5) pilgrimage for all able-bodied adults to Mecca--the Hajj. Additionally, there was a general directive to expand the universal religion, both through preaching and invitation to the faith, as well as by military conquest. Called the Lesser Jihad, it was only to be a junior partner to the Greater Jihad, consisting of inwardly directed self-improvement and spiritual contemplation.
These ideas were all presented as a verification and continuation of Judaism and Christianity, and as such, Islam was able to attract growing bodies of adherents, impressed with its self-justifying political successes. Of course, its comparative toleration of non-Muslims also facilitated territorial growth. Thus, as opposed to any other of the tribal migrant groups, Muslims were motivated by a program and an institution--the Calpihate--as opposed to individuals or mere material desires. At the same time, even during the conquests, a more settled Islamic civilization was being elaborated in the hinterland. Involving relatively advanced theological-legal institutions and juridical thinking, cultivation of trade both domestically and internationally, and the translation of ancient sciences as well as their extension, Islam in the cities provided a strong cultural basis for conquest and civilizational homogeneity. Though the Abbasid state had broken down by 1000, a Islamic World had emerged with common social, political, cultural, and economic assumptions throughout.
While Western and Central Europe were being ruled by mostly illiterate warrior thugs concerned only with control of land and booty, the Islamic states were administered by relatively sophisticated, pragmatic Amirs, who patronized culture, tolerated non-Muslims, and had evolved a common civilization, even though disparate states were emerging.