Long before men awoke to the vision of America, the Old World was the scene of many stupendous migrations. One after another, the Goths, the Huns, the Saracens, the Turks, and the Tatars, by the sheer tidal force of their numbers threatened to engulf the ancient and medieval civilization of Europe. But neither in the motives prompting them nor in the effect they produced, nor yet in the magnitude of their numbers, will such migrations bear comparison with the great exodus of European peoples which in the course of three centuries has made the United States of America.