Singular (Mawla); a non Arab embracing Islam and affiliating himself with an Arabian tribe to claim exemption from the taxes and social disabilities which befell all
non 'Muslims'.

       The Mawali were foreigners who had converted to Islam; because, however, they were foreigners, they could not be incorporated into the kinship-based society of Arabs. They had to be voluntarily included into the protection of a clan, that is, they had to become "clients" of the clan (which is what the word mawali means).

       For the most part, they were second-class citizens even though they were Muslims.

       The Mawla's ill-defined rank put him in an inferior position to the 'Muslim' Arabian. As their numbers grew with the expanding occupation and subjugation of enormous tracts of their lands by the conquering Arabs, so did their anger; after all, it was their land and they had a much higher civilization and culture than their conquerors, yet they were treated as if they were inferior.

        These were the heirs to the great civilizations of Persia and Byzantium. They became at the fore-front of further Arabian conquests as well as acting as the civil administrators of their own territiories on behalf of the uncivilized Arabians.

They were blatantly discriminated against in a variety of ways such as:

Their pay was less than their Arabian counterparts although they were doing the same jobs.

They were not allowed to marry Arabian women.

They were prohibited from buying land in Arabia although they are Muslims.

They received much less than they deserved from the booty that they gained from further conquests in which they were major participants.

Their Temples were destroyed by the Arabs.

Their Language was being replaced by Arabic.

Their ancient and great Religion was being replaced by that of the Arabs;
Muhammadan Islam.

Their glorious ancient History ceased to exist and thier new one started from the moment of their conquest and subjugation.

They were actually being INDOCTRINATED into the CULT of Muhammad and ARABIZED at the same time.

        All the above ingredients were excellent fuel for a subsequent revolution and uprising as in the 734-46 rebellion of al-Harith ibn Surayj in Khurasan (Persia) when the Mawali demanded fiscal equality, and equal pay with the Arabs.

`         The Abassids took their name from al-'Abbas, a paternal uncle of Muhammad and one of his early supporters. Their close kinship to Muhammad and the position of al-'Abbas as one of his Companions served them well in gaining support.

       As early as 718 AD, during the reign of Umar II, Muhammad ibn 'Ali, a great-grandson of al-'Abbas, began to proselytize in Persia to rally support for returning the caliphate to the family of Muhammad, the Hashimites.

          What made the 'Abassid seizure of the caliphate unique was the heavy reliance on client Muslims, or Mawali.

       In fact, it was during this period and there-after, that the Arabian dominance of Islam was completely overtaken by none Arabians.

Islamic Terms Dictionary         Mawla

A person of slave origin who does not have tribal protection.  It is a word with dual meaning. It can mean either master or servant.

4: 33        To (benefit) everyone We have appointed sharers and heirs [Mawla] to property left by parents and relatives.  To those also to whom your right hand was pledged give their due portion: for truly Allah is Witness to all things.

Sahih Al-Bukhari HadithHadith 6.104        Narrated byIbn Abbas
Regarding the Verse: "To everyone, We have appointed heirs."  (4.33) 'Mawali' means heirs. And regarding:   "And those to whom your right hands have pledged,"
When the Emigrants came to Medina, an Emigrant used to be the heir of an Ansari with the exclusion of the latter's relatives, and that was because of the bond of brotherhood which the Prophet had established between them (i.e. the Emigrants and the Ansar). So when the Verse:   "To everyone We have appointed heirs," was revealed, (the inheritance through bond of brotherhood) was cancelled. Ibn Abbas then said: "And those to whom your right hands have pledged," is concerned with the covenant of helping and advising each other. So allies are no longer to be the heir of each other, but they can bequeath each other some of their property by means of a will.