News of the U.S. victory traveled quickly across the United States. In the South, planters imagined slavery spreading into the lands acquired from Mexico. Northerners, too, applauded the expansion of U.S. territory but focused on California as a center for agriculture and commerce. Yet the acquisition of new territory only heightened sectional conflicts. Debates over slavery had erupted during the war, with a few northern Democrats joining Whigs in denouncing “the power of SLAVERY” to “govern the country, its Constitutions and laws.” In August 1846, Democratic congressman David Wilmot of Pennsylvania proposed outlawing slavery in all territory acquired from Mexico so that the South could not profit from the war. While the Wilmot Proviso passed in the House, southern and proslavery northern Democrats in the Senate killed it.

The presidential election of 1848 opened with the unresolved question of whether to allow slavery in the territories acquired from Mexico. With Polk declining to run for a second term, Democrats nominated Lewis Cass, a Michigan senator and ardent expansionist. Hoping to keep northern antislavery Democrats in the party, Cass argued that residents in each territory should decide whether to make the region free or slave. This strategy put the slavery question on hold but satisfied almost no one.

The Whigs, too, hoped to avoid the slavery issue for fear of losing southern votes. They nominated Mexican-American War hero General Zachary Taylor, a Louisiana slaveholder who had no declared position on slavery in the western territories. But they sought to reassure their northern wing by nominating Millard Fillmore of Buffalo, New York, for vice president. As a member of Congress in the 1830s, Fillmore had opposed the annexation of Texas.

The Liberty Party, disappointed in the Whig ticket, decided to run its own candidate for president. But leaders who hoped to expand their support reconstituted themselves as the Free-Soil Party. Its leaders focused more on excluding slaves from the western territories than on the moral injustice of slavery. The party nominated former president Martin Van Buren and appealed to small farmers and urban workers who hoped to benefit from western expansion.

Once again, the presence of a third party affected the outcome of the election. While Whigs and Democrats tried to avoid the slavery issue, Free-Soilers demanded attention to it. By focusing on the exclusion of slavery in western territories rather than its abolition, the Free-Soil Party won more adherents in northern states. Indeed, Van Buren won enough northern Democrats so that Cass lost New York State and the 1848 election. Zachary Taylor and the Whigs won, but only by placing a southern slaveholder in the White House.

REVIEW & RELATE

How did the battle over Texas affect relations among Indian nations, among white Americans, and between Indians and whites?

How did the Mexican-American War reshape national politics and intensify debates over slavery?