ABSTRACT
The civilisation whose development is rightly attributed to the spread of Islam was due partly, to the activity of peoples from Arabia, whose victorious emigration was accompanied by a parallel expansion of their language and their tradition. Islam's domination was expressed either by a multiplication in the number of towns or by an undeniable growth in population and area of ancient cities occupied by the conquerors, whether it was in Egypt, in the Maghrib, or in Spain, as in Syria, Iraq or Iran. On the other hand, it is certain that non–Arab invasions on a large scale on various occasions at the heart of the Islamic world came to disturb the relations between bedouin and sedentary peoples which had scarcely changed since the period of the first conquests, and also to leave their mark on all medieval Muslim history.
