Between the defeat of Mithridates and the triumph of Heraclius, the political geography of the Middle East underwent a series of profound changes. Many of these were driven by the interests and policies of the dominant states and empires of the time: Rome, Parthian and Sasanian Persia, Himyar, and, to a lesser extent, the kingdom of Aksum. The petty kingdoms, confederations, princely states, and wandering groups which had characterised the political map in the first century bc had, by the sixth century ce, almost completely vanished. Their disappearance was a result of imperial ambition, episodic bouts of interstate warfare and intercommunal religious violence, as well as the more prosaic realities of frontier politics and the changing demands of administrative arrangements.