Throughout the whole period there came against Europe, out of the unknown wastes of central Asia, an endless succession of strange and terrible conqueror races whose mission was mere destruction--Hun and Avar, Mongol, Tartar, and Turk. These fierce and squalid tribes of warrior horsemen flailed mankind with red scourges, wasted and destroyed, and then vanished from the ground they had overrun. But in no way worth noting did they count in the advance of mankind. At last, a little over four hundred years ago, the movement towards a world civilization took up its interrupted march. The beginning of the modern movement may roughly be taken as synchronizing with the discovery of printing, and with that series of bold sea ventures which culminated in the discovery of America; and after these two epochal feats had begun to produce their full effects in material and intellectual life, it became inevitable that civilization should thereafter differ not only in degree but even in kind from all that had gone before. Immediately after the voyages of Columbus and Vasco da Gama there began a tremendous religious ferment; the awakening of intellect went hand in hand with the moral uprising; the great names of Copernicus, Bruno, Kepler, and Galileo show that the mind of man was breaking the fetters that had cramped it; and for the first time experimentation was used as a check upon observation and theorization. Since then, century by century, the changes have increased in rapidity and complexity, and have attained their maximum in both respects during the century just past. Instead of being directed by one or two dominant peoples, as was the case with all similar movements of the past, the new movement was shared by many different nations. From every standpoint it has been of infinitely greater moment than anything hitherto seen. Not in one but in many different peoples there has been extraordinary growth in wealth, in population, in power of organization, and in mastery over mechanical activity and natural resources. All of this has been accompanied and signalized by an immense outburst of energy and restless initiative. The result is as varied as it is striking.