ABSTRACT
History records innumerable assaults by the barbarian nomads of the steppes and deserts on the realms of civilization. The Arab and Mongol conquests also raise the question why the former cleared the ground for the erection of a distinctive new world culture and the latter did not. It is doubtless true that the astonishing success of the Arab invaders was due partly to the weakness and disunity of the civilized states which were their chief targets of attack. The political anarchy which delivered Russia into Mongol hands resembles the confusion and fecklessness which allowed the Arabs to overturn the Visigothic kingdom in Spain in a single battle. The Nestorians, who had helped to educate the Arabs, were but poorly equipped to educate the Mongols, for they themselves had suffered a cultural decline in the intervening centuries, were more scattered and isolated and removed from the original sources of their intellectual life.
