▁the ▁sign ▁of ▁the ▁Black ▁Standard . ▁Close ▁to ▁ 1 0 , 0 0 0 ▁soldiers ▁were ▁under ▁Ab u ▁Muslim ' s ▁command ▁when ▁the ▁host ilities ▁officially ▁began ▁in ▁Mer v . ▁ ▁Leg acy ▁ ▁Further ▁con quest ▁ ▁After ▁the ▁Abb as id ▁took ▁over ▁the ▁Kh uras an , ▁various ▁new ▁generation ▁of ▁Muslim ▁D ynast y ▁and ▁v ass al ▁kingdom s ▁was ▁emer ging ▁and ▁continued ▁the ▁second ▁wave ▁of ▁Muslim ▁con quest ▁to ▁the ▁east . ▁at ▁first ▁it ▁was ▁given ▁by ▁the ▁Abb as id ▁under ▁the ▁rule ▁Author ity ▁of ▁S aff ar ids , ▁a ▁Muslim ▁Pers ian ate ▁dynast y ▁from ▁S istan ▁that ▁ruled ▁over ▁parts ▁of ▁eastern ▁Iran , ▁K hor as an , ▁Afghan istan ▁and ▁Bal och istan ▁from ▁ 8 6 1 ▁to ▁ 1 0 0 3 . ▁The ▁dynast y , ▁of ▁Pers ian ▁origin , ▁was ▁founded ▁by ▁Ya ' qu b ▁bin ▁La ith ▁as - S aff ar , ▁a ▁native ▁of ▁S istan ▁and ▁a ▁local ▁a yy ā r , ▁who ▁worked ▁as ▁a ▁co ppers m ith ▁( ṣ aff ā r ) ▁before ▁becoming ▁a ▁war l ord . ▁He ▁seized ▁control ▁of ▁the ▁S istan ▁region ▁and ▁began ▁conqu ering ▁most ▁of ▁Iran ▁and ▁Afghan istan , ▁as ▁well ▁as ▁parts ▁of ▁Pakistan , ▁T aj ik est an ▁and ▁U z bek istan . ▁ ▁In ▁ 9 0 1 , ▁Am r ▁S