384 THE PULSE OF ASIA
at first to the influence of improved climatic conditions, until it, too, was reached by the migrating hordes of invaders. Meanwhile, in the most densely populated part of Arabia, another movement of the nations had begun, presumably because of the distress due to rapid desiccation. The Arab migrants carried with them the fanatical faith of Mohammed, and were by it inspired to remoter conquests. The migrants to Europe found there Christianity, and in time became its greatest exponents.
When the progress of desiccation was stayed in Asia, and the desert lands began to grow slightly more habitable, there was no further impulse impelling migration, and Europe was freed from further invasion. At last, at the beginning of the Middle Ages, she was free to develop in response to the favorable climatic conditions which had come upon her. Christianity and the civilization to which it gives name and form found a fruitful field of development, one which has continued to expand. Mohammedanism, too, was able to make progress for a time during the period of revival accompanying the expansion of the habitable areas of Persia, Syria, and other parts of Central Asia' and north Africa. Under the Caliphs, Mohammedan civilization progressed more rapidly than did that of Christian Europe, but soon the climate ceased to become more favorable, and stagnation ensued, followed by retrogression, when a slight tendency toward desiccation again appeared.
To-day, the strongest nations of the world live where the climatic conditions are most propitious. Japan and north China in Asia; Russia, Austria, Germany, France, and England in Europe; and the United States and Canada in
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