What is the name of the geographical region that early Islamic usage often regarded everywhere east of western Persia and where Vistaham helped Khosrow regain his throne after the rebellion of Bahram Chobin?
Vistahm Bistam or Vistahm (also transliterated Wistaxm, Persian: بیستام‎ ‎ ), was a Parthian dynast of the Ispahbudhan house, and maternal uncle of the Sasanian "shah" of Persia, Khosrow II (reigned 591–628). Vistahm helped Khosrow regain his throne after the rebellion of Bahram Chobin, but later led a revolt himself, which encompassed the entire Iranian East before being suppressed.
Al-Muwaffaq Abu Ahmad Talha ibn Ja'far (Arabic: أبو أحمد طلحة بن جعفر‎ ‎ ) (842 – June 2, 891), better known by his "laqab" as al-Muwaffaq bi-Allah (Arabic: الموفق بالله‎ ‎ , "Blessed of God" ), was an Abbasid prince and military leader, who acted as the virtual regent of the Abbasid Caliphate for most of the reign of his brother, Caliph al-Mu'tamid. His stabilization of the internal political scene after the decade-long "Anarchy at Samarra", his successful defence of Iraq against the Saffarids and the suppression of the Zanj Rebellion restored a measure of the Caliphate's former power and began a period of recovery, which culminated in the reign of al-Muwaffaq's own son, the Caliph al-Mu'tadid.