John M. Murrin, et al., eds., Liberty Equality Power: A History of the American People, 2nd ed., vol. 1 (Fort Worth: Harcourt Brace, 1999), 435-36.
Many Americans in 1850 took this prodigious growth for granted. They considered it evidence of God’s beneficence to this virtuous republic, this haven for the oppressed seeking refuge from Old World tyranny, this land where all (white) men stood equal before the law. During the 1840s a group of expansionists affiliated with the Democratic Party began to call themselves the “Young America” movement. They proclaimed that it was the “Manifest Destiny” of the United States to grow from sea to sea, from the Arctic Circle to the tropics. It is “our manifest destiny to overspread and to possess the whole of the continent which Providence has given us for the development of the great experiment of liberty,” wrote John L. O’Sullivan, editor of the Democratic Review, in 1845. “Yes, more, more, more!...till our national destiny is fulfilled and…the whole boundless continent is ours.” Not all Americans thought this unbridled expansion was a good thing. For the earliest Americans, whose ancestors had arrived on the continent thousands of years before the Europeans, it was a story of defeat and contraction rather than of conquest and growth. By 1850 the white man’s diseases and guns had reduced the Indian population north of the Rio Grande to fewer than half a million, a fraction of the number who had lived there two or three centuries earlier. The relentless westward march of white settlement had pushed all but a few thousand Indians beyond the Mississippi.