The advent of Islam in Arabia created a new regional actor: the Rashidun Caliphate. Later caliphates inherited the vast territories of expansion accrued under the Rashidun. The ordeal of civil war was the crucible from which the Umayyad Caliphate arose. Civil crisis had a lasting influence on both the strategic setting and then environment within which successive Umayyad and Abbasid caliphs had to contend. Unity and unification of the caliphate was a necessary political objective for the duration of all caliphates. The Umayyads fused their right to political legitimacy with their military prowess and notions of divine providence. The ideological dependency of the Umayyad Caliphate to an aggressive policy of security-maximising expansionism was predicated upon a politically legitimating doctrine of perpetual war which constantly directed strategic decision making. The dependency upon war serving as the only strategic instrument subordinated to the political ends of security, the Umayyad leadership was distracted from managing growing internal dissent and covert factions brewing rebellion and eventual revolution. The Abbasid Revolution of AD 750 not only ended the Umayyad House, but effectively sheathed the doctrine of perpetual war that the Umayyad Caliphate had wielded for nearly a century. The Abbasids squandered the vast territorial and strategic inheritance within decades of wrestling power. The early course of the Rashidun, Umayyad and Abbasid caliphates, was consistently one of political and territorial expansion followed by structural fragmentation, civil strife and subsequent collapse.