Parthia was a north-eastern Iranian satrapy of the Achaemenid empire which later passed on to Alexander's empire. Under the Seleucids, Parthia was governed by various Greek satraps such as Nicanor and Philip (satrap). In 247 BC, following the death of Antiochus II Theos, Andragoras, the Seleucid governor of Parthia, proclaimed his independence and began minting coins showing himself wearing a royal diadem and claiming kingship. He ruled until 238 BCE when Arsaces, the leader of the Parni tribe conquered Parthia, killing Andragoras and inaugurating the Arsacid Dynasty. Antiochus III recaptured Arsacid controlled territory in 209 BC from Arsaces II. Arsaces II sued for peace became a vassal of the Seleucids and it was not until the reign of Phraates I (168–165 BCE), that the Arsacids would again begin to assert their independence.
What tribe was Arsaces the leader of? (If the question is unanswerable, say "unanswerable")
Parni