Traversing the continent "from sea to shining sea" was hardly a natural westward procession of covered wagons as portrayed in Western movies. The US invasion of Mexico was carried out by US marines, by sea, through Veracruz, and the early colonization of California initially progressed from the Pacific coast, reached from the Atlantic coast by way of Tierra del Fuego. Between the Mississippi River and the Rockies lay a vast region controlled by Indigenous nations that were neither conquered nor colonized by any European power, and although the United States managed to annex northern Mexico, large numbers of settlers could not reach the Northern California goldfields or the fertile Willamette Valley region of the Pacific Northwest without army regiments accompanying them. Why then does the popular US historical narrative of a "natural" westward movement persist? The answer is that those who still hold to the narrative remain captives of the ideology of "manifest destiny," according to which the United States expanded across the continent to assume its preordained size and shape. This ideology normalizes the successive invasions and occupations of Indigenous nations and Mexico as not being colonialist or imperialist, rather simply ordained progress. In this view, Mexico was just another Indian nation to be crushed.

— An Indigenous Peoples' History of the United States (ReVisioning American History) by Roxanne Dunbar-Ortiz, Roxanne Dunbar Ortiz (Page 118)