Southerners eager to expand the plantation economy were at the forefront of the push for territorial expansion. Yet expansion was not merely a southern strategy. Northerners demanded that the United States reject British claims to the Oregon Territory, and some northern politicians and businessmen advocated acquiring Hawaii and Samoa to benefit U.S. trade. In 1844 the Democratic Party built on these expansionist dreams to recapture the White House.

The Democrats nominated a Tennessee congressman and governor, James K. Polk. The Whigs, unwilling to nominate Tyler for president, chose Kentucky senator Henry Clay. Polk declared himself in favor of the annexation of Texas. Clay, meanwhile, waffled on the issue. This proved his undoing when the Liberty Party, a small antislavery party founded in 1840, denounced annexation. Liberty Party candidate James G. Birney captured just enough votes in New York State to throw the state and the election to Polk.

In February 1845, a month before Polk took office, Congress passed a joint resolution annexing the Republic of Texas. That summer, John L. O’Sullivan, editor of the Democratic Review, captured the American mood by declaring that nothing must interfere with “the fulfillment of our manifest destiny to overspread the continent allotted by Providence.” This vision of manifest destiny—of the nation’s God-given right to expand its borders—defined Polk’s presidency.

With the Texas question seemingly resolved, President Polk turned his attention to Oregon, which stretched from the forty-second parallel to latitude 54°40' and was jointly occupied by Great Britain and the United States.

In 1842, three years before Polk took office, glowing reports of the mild climate and fertile soil around Puget Sound had inspired thousands of farmers and traders to flood into Oregon’s Willamette Valley. Alarmed by this “Oregon fever,” the British tried to confine Americans to areas south of the Columbia River. But U.S. settlers demanded access to the entire territory. President Polk encouraged migration into Oregon but was unwilling to risk war with Great Britain. Instead, diplomats negotiated a treaty in 1846 that extended the border with British Canada (the forty-ninth parallel) to the Pacific Ocean. Over the next two years, Congress admitted Iowa and Wisconsin to statehood, reassuring northern residents that expansion benefited all regions of the nation.

Many of the lands newly claimed by the U.S. government were home to vast numbers of Indians. Indeed, the West had become more crowded as the U.S. government forced eastern tribes to move west of the Mississippi (see Map 10.2). When the Cherokee and other southeastern tribes were removed to Indian Territory, for example, they confronted tribes such as the Osage. Pushed into the Southwest, the Osage came into conflict with the Comanche, who had earlier fought the Apache for control of the southern plains. Other Indian nations were pushed onto the northern plains from the Old Northwest. When tribes like the Mandan were decimated by smallpox in the 1830s, the Sioux dominated the region.

The flood of U.S. migrants into Texas and the southern plains transformed relations among Indian nations as well as with Mexico. In the face of Spanish and then Mexican claims on their lands, for example, the Comanche forged alliances with former foes like the Wichita and the Osage. The Comanche also developed commercial ties with tribes in Indian Territory and with both Mexican and Anglo-American traders. They thereby hoped to benefit from the imperial ambitions of the United States and Mexico while strengthening bonds among Indians in the region.

Comanche expansion was especially problematic for Mexico. The young nation did not have sufficient resources to sustain the level of gift giving that Spanish authorities had used to maintain peace. As a result, Comanche warriors launched continual raids against Tejano settlements in Texas. But the Comanche also developed commercial relations with residents of New Mexico, who flaunted trade regulations promulgated in Mexico City. By 1846 Comanche trade and diplomatic relations with New Mexican settlements had seriously weakened the hold of Mexican authorities on their northern provinces.