What happened on this land around c. 200–100 BCE?

Expansion of Parthians; decline of Seleucid influence; Iran becomes core of Arsacid power.
Rulers
Parthian (Arsacid) Empire
247 BCE–224 CE
Parthians gradually supplant Seleucids in Iran.
Battles
Battle of Magnesia
190 BCE
Romans defeat Seleucids, weakening Hellenistic control in Asia.