Axidares was a son of the Parthian king Pacorus II (r.78-105), who had made his son king of Armenia, a buffer state that had caused several conflicts between the Parthians and Romans. A compromise had been found: the Roman emperor would crown the Armenian king, who would be a member from the Parthian Arsacid family. So, Axidares was as king officially recognized by both sides.
He appears to have been a weak ruler, because after Pacorus' death in 105 CE, his brother and successor Osroes I felt himself forced to dethrone his nephew. This was a situation that had never been considered before. The Roman emperor Trajan (r.98-117) decided to intervene, which the Parthians had not unexpected. The Graeco-Roman historian Cassius Dio summarizes what Parthian envoys, trying to avoid war, said:
When Trajan had set out against the Parthians and got as far as Athens, an embassy from Osroes met him, asking for peace and proffering gifts. ... At the same time he asked that Armenia be given to Parthamasiris, who was likewise a son of Pacorus, and requested that the diadem be sent to him; for he had deposed Axidares, he said, inasmuch as he had been satisfactory neither to the Romans nor to the Parthians.note[Cassius Dio, Roman History 68.17.2; tr. Earnest Cary.]
In other words, Osroes recognized that Rome was to crown the king of Armenia, and he had only removed a bad ruler (his nephew Axidares), so that a better man (his brother Parthamasiris) could occupy the throne. Trajan was not impressed. In 114, he invaded Armenia, accepted the surrender of Parthamasiris, and converted the kingdom into a Roman province.note[Cassius Dio, Roman History 68.19.]