Westward Expansion (1807-1912): The Mexican War and Political Aftermath

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By the end of the Mexican War, the spirit of expansion was especially strong. Some in Congress decried the Treaty of Guadalupe Hidalgo because it did not cede all of Mexico to the US after the resounding US victory. Others, however, argued that the racial impurity of Mexican inhabitants would lead to calamity. Thus, racism allowed Mexico to maintain its sovereignty.

As for the question of slavery in the West, which became the singular focus of US politics after the Mexican War, Polk believed that expansion would preserve the agricultural and democratic nature of the US, and weaken tendencies toward centralized power. He believed these benefits to be the paramount goal of westward expansion, and believed they would be reaped whether the new territory was free or slave. He saw the Missouri Compromise, which prohibited slavery in all land north of 36 degrees 30 minutes latitude, as a sufficient solution to the issue of slavery. Some antislavery Whigs vehemently disagreed, especially abolitionists from New England and Ohio, opposed the extension of slavery into the territories on moral grounds. However, a more important challenge to the expansion of slavery came from northern Democrats who feared that extending slavery into New Mexico and California would deter free laborers from settling there. They argued that deterring migration to the West would intensify class struggle in the East. David Wilmot fell into this second category. He was not an abolitionist, nor did he seek to split his party. He simply spoke for the northern Democrats who had been led to believe that Texas would be the last slave state. Polk and his cabinet had given the impression that Texas would be for the slaveholders and California and New Mexico for free labor.

The issue of slavery in the territories raised some questions of Constitutionality. John Calhoun and his followers asserted that since slaves were property, they should be protected in all areas by the Constitution, meaning that the Missouri Compromise was unconstitutional and slaveholders could take their slaves anywhere they wished. Northerners, on the other side, cited the history of regulation of slavery by the federal government and the wording of the Constitution, which gave Congress the power to "make all needful rules and regulations respecting the territory or other property of the United States." Politicians searched for a middle ground but more often than not found only morass and deadlock. The increasing expansion into the territories of the West, largely due to the gold rush, made the search for compromise all the more frantic.

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