Most Americans believed that the superiority of their institutions and white culture bestowed on them a God-given right to spread across the continent. They imagined the West as a howling wilderness, empty and undeveloped. If they recognized Indians and Mexicans at all, they dismissed them as primitives who would have to be redeemed, shoved aside, or exterminated. The West provided young men especially an arena in which to “show their manhood.” Most Americans believed that the West needed the civilizing power of the hammer and the plow, the ballot box and the pulpit, which had transformed the East.

In 1845, a New York political journal edited by John L. O’Sullivan coined the term manifest destiny to justify white settlers taking the land they coveted. O’Sullivan called on Americans to resist any effort to thwart “the fulfillment of our manifest destiny to overspread the continent allotted by Providence for the free development of our yearly multiplying millions … [and] for the development of the great experiment of liberty and federative self-government entrusted to us.” Almost overnight, the magic phrase manifest destiny swept the nation, providing an ideological shield for conquering the West.

As important as national pride and racial arrogance were to manifest destiny, economic gain made up its core. Land hunger drew hundreds of thousands of Americans westward. Some politicians, moreover, had become convinced that national prosperity depended on capturing the rich trade of the Far East. To trade with Asia, the United States needed the Pacific coast ports that stretched from San Diego to Puget Sound. The United States and Asia must “talk together, and trade together,” Missouri senator Thomas Hart Benton declared. “Commerce is a great civilizer.” In the 1840s, American economic expansion came wrapped in the rhetoric of uplift and civilization.