"It is not generally appreciated how the success of Luther's religious revolution against Catholicism in Germany was due to the way in which Mohammedan pressure from the East was paralysing the central authority of the German Emperors. They had to compromise with the leaders of the religious revolution and try to patch up a sort of awkward peace between the irreconcilable claims of Catholic authority and Protestant religious theory in order to meet the enemy at their gates; the enemy which had already overthrown Hungary and might well overthrow all of Southern Germany and perhaps reach the Rhine. If Islam had succeeded in doing this during the chaos of violent civil dissension among the Germans, due to the launching of the Reformation, our civilization would have been as effectively destroyed as it would have been if the first rush of the Mohammedans through Spain had not been checked and beaten back eight centuries earlier in the middle of France."
~Hilaire Belloc: The Great Heresies, Chap. III.