FTP, name this Middle-Eastern empire, which preceded the Sassanids as rulers of Persia.
This empire often had trouble keeping its great families such as Karin, Gev, and Suren in check and its administration has often been described as "feudal."  Notable rulers include Vologeses I, who sought to put a puppet ruler up in Aremnia and earned the ire of Rome.  Ruled by the Arsacid dynasty, this empire was defeated in campaigns by Trajan and Septimius Severus, but did succeed in defeating and killing Crassus a Carrhae.  FTP, name this Middle-Eastern empire, which preceded the Sassanids as rulers of Persia.
This empire often had trouble keeping its great families such as Karin, Gev, and Suren in check and its administration has often been described as "feudal."  
Parthians or Parthia (accept Arsacids before mentioned).