Meanwhile, the Seleucid positions in the eastern Upper Satrapies, already weakened by the previous kings' failure to contain the Parthians and the Greco-Bactrians, suffered almost complete collapse. The Parthians under Mithridates I took advantage of the general instability to invade Media.
The Seleucid forces in the eastern Upper Satrapies, already weakened by previous kings' inability to contain the Parthians and Greco-Bactrians, were vulnerable to attack by the Parthians under Mithridates I.