The Romans respected the Parthians and their military skills, ever since their general Crassus suffered a crushing defeat to them
at Carrhae in 55 BC. The Parthians, on the other hand, were waiting for the Romans to reveal weaknesses that would enable them to regain their former strength on the eastern border of the Roman empire.
The Jews respected the existing power balance: that meant Roman rule. However they hoped for a shift in the regional balance of power in favour of the Parthians, and for increased autonomy for the small Jewish states under Parthian dominance.
When Matt. 26:53 mentions twelve legions of angels coming to support Jesus, the writer is thinking precisely of the Parthian archers. The Parthians supported the Jews’ rebellions against Rome.
The latent conflict between Romans and Parthians led to military operations during the Armenian crisis in 35 – 36 AD, giving brief hope of an end to Roman rule in Palestine.