After the death of his father, Antiochus II, in 246 BC, Seleucus II succeeded him as ruler, but was unable to respond to the Parthian raids in the Eastern portion of the empire due to war with Ptolemaic Egypt and, subsequently, his younger brother, Hierax, who attempted to establish himself as the independent ruler of Asia Minor. Eventually, the two brothers reached a truce and Seleucus was able to begin an expedition against the Parthians. Despite achieving initial success, expelling the Parthians from Parthia and Hyrcania, Seleucus II was likely defeated and possibly captured by the Parthians, who were possibly aided by Diodotus II, the ruler of Bactria.