All this being so, the course of deciding that the Arabs retrogressed because "they" were impatient and discontinuous is on a level with the thesis that nature has a horror of a vacuum. The Arab civilisation was arrested and anchylosed by forces which in other civilisations operated in exactly the same modes. The first great trouble was the element of perpetual domestic strife, which was uncured by the monarchic system, since every succession was liable to dispute. Under such conditions just government could not flourish; and Moslem taxation always tended to be suicidally unscrupulous.[387] Disputes of succession, indeed, wrought hardly more strife among the Saracens than has taken place among Greeks and Romans, and Christians of all nations, down to modern times; even the ecclesiastical and feudal doctrine of legitimacy, developed by the Latin and Greek Churches, having failed to prevent dynastic wars in Christendom. But the Saracens, neighboured everywhere by Christians who bore them a twofold hostility, had peculiar need of union, and ran special risks from dissension; and in Spain their disunion was their ruin. At the same time their civilisation was strangled intellectually by a force which, though actually in operation in Christendom also, was there sufficiently countered by a saving condition which the Saracens finally lacked. The force of constriction was the cult of the Sacred Book; the counteracting force in Christendom was diversity and friction of governments and cultures--a condition which passed out of the Saracen equation.