It is a common assumption that the Arab conquests were fuelled by the impulse of Islamic proselytism, an assumption perhaps the result of erroneously evaluating the nature of the Arab conquering process as an unchanging function since its outset. Indeed, Mohammad's aggressive campaign, consisting of a series of battles, some of which may have been exercises in political strategy, was as a whole probably intended to spread his beliefs among the Arab peoples. However, the important question is in then ascertaining whether the ensuing continuation of this expansionist tendency throughout the Middle East, undertaken by the Prophet's successors, was a carrying forth of the Prophet's example of proselytism or whether it became an outward tendency of mainly political momentum.
The extent to which the Arab Muslims who came to hold power in the cities of the Middle East actively engaged in proselytism presents a misleading picture. The practices in Arab jurisdiction which appear to have discriminated against the dhimmi, those who had not converted, were mainly fiscal and centred on the jizya, the poll tax that non-Muslims had to pay and from which they could become exempt only through conversion.
There were examples of more far-reaching discriminatory practice against Jews and Christians such as segregation and denial of certain civil rights, but these instances are not illustrative of a concerted pressure to convert - they were more likely symbolic than practical, asserting the superiority of Muslims over practitioners of other faiths. Generally speaking, the kind of fiscal policy as set down by 'Umar II, whereby the jizya brought non-Muslims to protected civil status, albeit without any official ownership of the property on which they lived, prevailed in regimes to follow.
The actual purpose of jizya is yet another moot point; The Hadith of Shaih Muslim reports Mohammed as saying:...