Christopher Dawson, in The Origins of Europe, regards religious enthusiasm as the essential cause of Muslim victories, and Henri Pirenne, in Muhammed and Charlemagne, explains the Muslim success as follows: "The Arab conquest, which brought confusion upon both Europe and Asia, was without precedent. The swiftness of its victory is comparable only with that by which the Mongol Empires of Attila, Jenghiz Khan and Tamerlane were established. But these empires were as ephemeral as the conquest of Islam was lasting. This religion still has its faithful today in almost every country where it was imposed by the first Caliphs. The lightning-like rapidity of its diffusion was a veritable miracle as compared with the slow progress of Christianity . . the Arabs were exalted by a new faith . . . they were not even fanatical, and they did not expect to make converts of their subjects" (Henri Pirenne, Mohammed and Charlemagne, tr. Bernard Miall [reprinted; New York: Meridian Books, 1961], pp. 149-150).