The vast expansion of territory to more than threefold the great original domain of the United States had been made by honorable purchase or less honorable conquest. It had not added largely to the population of the nation; the new acquisitions were mainly of unoccupied land. The increase of the population, down to about 1845, was chiefly the natural increase of a hardy and prolific stock under conditions in the highest degree favorable to such increase. Up to the year 1820 the recent immigration had been inconsiderable. In the ten years 1820-29 the annual arrival of immigrants was nine thousand. In the next decade, 1830-39, the annual arrival was nearly thirty-five thousand, or a hundred a day. For forty years the total immigration from all quarters was much less than a half-million. In the course of the next three decades, from 1840 to 1869, there arrived in the United States from the various countries of Europe five and a half millions of people. It was more than the entire population of the country at the time of the first census;--
A multitude like which the populous North Poured never from her frozen loins to pass Rhene or the Danaw, when her barbarous sons Came like a deluge on the South and spread Beneath Gibraltar to the Libyan sands.
Under the pressure of a less copious flood of incursion the greatest empire in all history, strongest in arts and polity as well as arms, had perished utterly. If Rome, with her population of one hundred and twenty millions, her genius for war and government, and her long-compacted civilization, succumbed under a less sudden rush of invasion, what hope was there for the young American Republic, with its scanty population and its new and untried institutions?[316:1]
An impressive providential combination of causes determined this great historic movement of population at this time. It was effected by attractions in front of the emigrant, reinforced by impulses from behind. The conclusion of the peace of 1815 was followed by the beginning of an era of great public works, one of the first of which was the digging of the Erie Canal. This sort of enterprise makes an immediate demand for large forces of unskilled laborers; and in both hemispheres it has been observed to occasion movements of population out of Catholic countries into Protestant countries. The westward current of the indigenous population created a vacuum in the seaboard States, and a demand for labor that was soon felt in the labor-markets of the Old World. A liberal homestead policy on the part of the national government, and naturalization laws that were more than liberal, agencies for the encouragement of settlers organized by individual States and by railroad corporations and other great landed proprietors, and the eager competition of steamship companies drumming for steerage passengers in all parts of Europe--all these coöperated with the growing facility and cheapness of steam transportation to swell the current of migration. The discovery of gold in California quickened the flow of it.