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.