After the reign of Artaxias III Zeno, a Pontic prince who had been made king of Armenia in 18 CE by the Roman prince Germanicus, the Parthian king Artabanus II (r.10-38) intervened and made his son Arsaces king (34 CE). This was an interference in the affairs of the Roman Empire, because it was the Roman emperor who was supposed to appoint kings in Armenia.
As a countermeasure, the Roman governor in Syria, Lucius Vitellius, invited Mithridates, a brother of the king of the West-Caucasian state of Iberia (modern Georgia), to seize the Armenian throne. The result was a full-scale war between the Armenians and Iberians, in which nomads from Central Eurasia played a role as well. When king Artabanus of Parthia tried to intervene, Vitellius ordered his legions (III Gallica, VI Ferrata, X Fretensis and XII Fulminata) to prepare for war (late 35?). This was too much for Artabanus, who backed off and accepted the pro-Roman Mithridates of Iberia as the new king of Armenia. He was to reign from 36 to 51 CE.
Arsaces had been the first member of the Arsacid dynasty on the Armenian throne.