Moreover, above all the material resources of field, forest, and mountain, he was glad for the human stream which was flowing into America to fertilize them. The thrifty people who were shrewd and bold enough to come over from Great Britain and northern Europe were to profit by nature's gifts, and in the experience were to be welded "into one of the finest systems of population which has ever appeared." If it is fair to say that the history of immigration to America falls into three general periods, Crèvecoeur was writing about the very midst of the middle period, from 1675 to 1875. First had been a half century when only the strongest spirit of adventure or the strongest desire for freedom could impel men to attempt the conquest of an untried world. Every Englishman who came over and every American born here was conscious of the need of more hands to work, and all were eager for more Englishmen, and yet more, to help in the gigantic undertaking. In the last forty years, with the taking up of all the available land and the manning of the industries, the millions who have flooded in, not alone from England or Great Britain but mainly from southern Europe and the near East, have arrived as new mouths to feed. The problem has been not so much how they could help America as how America could take care of them; and with their arrival a feeling of perplexity and alarm has arisen such as was expressed in 1892 by Thomas Bailey Aldrich in his "Unguarded Gates": ... Wide open and unguarded stand our gates, And through them presses a wild motley throng-- Men from the Volga and the Tartar steppes, Featureless figures of the Hoang-Ho, Malayan, Scythian, Teuton, Kelt, and Slav, Flying the Old World's poverty and scorn; These bringing with them unknown gods and rites, Those, tiger passions here to stretch their claws. In street and alley what strange tongues are loud, Accents of menace alien to our air, Voices that once the Tower of Babel knew! O Liberty, white Goddess! is it well To leave the gates unguarded? ... Have a care Lest from thy brow the clustered stars be torn And trampled in the dust.... But Crèvecoeur was living between these two periods. The first conquest of the Eastern woods and fields had been made. America was known to be a land of plenty, and as yet there was more than plenty for all the newcomers from England and the neighboring countries of northern Europe. There seemed to be no limit to its resources. And so he wrote: