RELIGION, as we have seen, had made possible the organization of Medina. This organization united the scattered Arabs in military conquest; out of this community grew a state. The key to the movement is to be found in the character of the immediate successors of Mahomet. His death was followed by a general rising in Arabia against the domination of Medina, and Islam seemed destined at this time to succumb before an overwhelming reaction of tribal feeling and particularist tendencies. The situation was saved by the strong and ruthless generals who led the Medinese forces against the peoples of Central Arabia; they, and not the contemplatives of Islam, directed the course of the movement. In swift and merciless campaigns they gained ascendancy over the whole peninsula, uniting the warring elements in a loose confederation, organized for aggressive action. But before the subjection of Arabia was complete, the earliest raids on Syria and Iraq, undertaken only with small forces, and with little idea of regular conquest, had carried all before them, and the overwhelming victories of the Yarmuk and Kadesíya1 had made it possible for the newly formed confederacy to avoid disruption by launching its masses upon the neighbouring territories. The time was ripe for such an adventure, and the nearest outlet for the surging forces was the land that lay immediately north of the peninsula, between the empires of Rome and Persia.
Neither power was in. a position to offer organized resistance. A period of anarchy in the Sasanid domains had followed the triumphs of Heraclius, and when order was finally restored, it came too late. The situation of the Roman Empire, apparently so brilliant, needs more explanation. Her victories had not only rendered Persia a defenceless victim; they had at the same time so weakened her own resources that in less than eight years all her newly regained territory in Syria and Egypt was lost to her. One important reason for this speedy reversal of fortune was the decadence of her military power. Long campaigns had spoilt____________________