In the years immediately before the war, Parthia was roiled by a conflict between the two sons of King Vologases V. Vologases VI succeeded his father in 208 but his brother Artabanus V rebelled and declared himself king soon afterwards. While Artabanus eventually gained the upper hand, though without totally defeating his brother, the conflict destabilised the neighbouring kingdoms of Armenia and Osroene in the buffer zone between the Roman and Parthian Empires. Caracalla exploited civil strife in both kingdoms in order to expand Roman power in the region and set the scene for an advance into Parthia.[4] As Armenia and Osroene were both in the Parthian sphere of influence at this time – Armenia had swung between being either a Roman or a Parthian client state for over a century – he evidently saw an establishment of Roman domination as being a way of reducing Parthian power and positioning himself for an eventual move against Parthia itself.[5]