y ad ▁C ali ph ate ▁had ▁four ▁main ▁social ▁classes : ▁ ▁Muslim ▁Arab s ▁ ▁Muslim ▁non - A rab s ▁( cli ents ▁of ▁the ▁Muslim ▁Arab s ) ▁ ▁D h imm is ▁( non - Mus lim ▁free ▁persons ▁such ▁as ▁Christians , ▁Jews ▁and ▁Z oro ast ri ans ) ▁ ▁S la ves ▁ ▁The ▁Muslim ▁Arab s ▁were ▁at ▁the ▁top ▁of ▁the ▁society ▁and ▁saw ▁it ▁as ▁their ▁duty ▁to ▁rule ▁over ▁the ▁conquer ed ▁areas . ▁Despite ▁the ▁fact ▁that ▁Islam ▁teach es ▁the ▁equality ▁of ▁all ▁Muslim s , ▁the ▁Arab ▁Muslim s ▁held ▁themselves ▁in ▁higher ▁este em ▁than ▁Muslim ▁non - A rab s ▁and ▁generally ▁did ▁not ▁mix ▁with ▁other ▁Muslim s . ▁ ▁As ▁Islam ▁spread , ▁more ▁and ▁more ▁of ▁the ▁Muslim ▁population ▁consisted ▁of ▁non - A rab s . ▁This ▁caused ▁social ▁un rest , ▁as ▁the ▁new ▁converts ▁were ▁not ▁given ▁the ▁same ▁rights ▁as ▁Muslim ▁Arab s . ▁Also , ▁as ▁convers ions ▁increased , ▁tax ▁reven ues ▁from ▁non - Mus lim s ▁decre ased ▁to ▁dangerous ▁l ows . ▁These ▁issues ▁continued ▁to ▁w ors en ▁until ▁they ▁helped ▁cause ▁the ▁Abb as id ▁Revol t ▁in ▁the ▁ 7 4 0 s . ▁ ▁Non - Mus lim s ▁Non - Mus lim ▁groups ▁in ▁the ▁Um ay y ad ▁C ali ph ate , ▁which ▁included ▁Christians , ▁Jews , ▁Z oro ast ri ans ▁and ▁pag ans ,