, ▁incorpor ating ▁the ▁Trans ox iana , ▁S ind h , ▁the ▁Mag h reb ▁and ▁the ▁I ber ian ▁Pen ins ula ▁( Al - And alus ) ▁into ▁the ▁Muslim ▁world . ▁At ▁its ▁greatest ▁extent , ▁the ▁Um ay y ad ▁C ali ph ate ▁covered ▁ ▁and ▁ 3 3   mill ion ▁people , ▁making ▁it ▁one ▁of ▁the ▁largest ▁emp ires ▁in ▁history ▁in ▁both ▁area ▁and ▁proportion ▁of ▁the ▁world ' s ▁population . ▁ ▁The ▁dynast y ▁was ▁eventually ▁over th rown ▁by ▁a ▁re bell ion ▁led ▁by ▁the ▁Abb as ids ▁in ▁ 7 5 0 . ▁Sur viv ors ▁of ▁the ▁dynast y ▁established ▁themselves ▁in ▁Cord oba ▁which , ▁in ▁the ▁form ▁of ▁an ▁Em ir ate ▁and ▁then ▁a ▁C ali ph ate , ▁became ▁a ▁world ▁centre ▁of ▁science , ▁medicine , ▁philosophy ▁and ▁in vention , ▁us her ing ▁in ▁the ▁period ▁of ▁the ▁Golden ▁Age ▁of ▁Islam . ▁ ▁The ▁Um ay y ad ▁cal i ph ate ▁ruled ▁over ▁a ▁vast ▁multi eth nic ▁and ▁mult icult ural ▁population . ▁Christians , ▁who ▁still ▁constit uted ▁a ▁majority ▁of ▁the ▁C ali ph ate ' s ▁population , ▁and ▁Jews ▁were ▁allowed ▁to ▁practice ▁their ▁own ▁religion ▁but ▁had ▁to ▁pay ▁a ▁head ▁tax ▁( the ▁j iz ya ) ▁from ▁which ▁Muslim s ▁were ▁ex empt . ▁There ▁was , ▁however , ▁the ▁Muslim - only ▁zak at ▁tax , ▁which ▁was ▁ear mark