Western Expansion, Manifest Destiny, and the Mexican-American War

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What were the political effects of Manifest Destiny in the United States?

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Manifest Destiny is an expression that first appeared in an 1845 Democratic Review editorial to describe the drive toward obtaining land in order to expand the boundaries of United States territory. The term is generally thought to be originated by editor John O’Sullivan. Those who supported this concept believed that it was God’s destiny for Americans to spread their principles of authority, democracy and capitalism across the entire North American continent, which had commenced with the Louisiana Purchase in 1803.

It spurred the move toward gobbling up large parcels of land, including the annexation of Texas and the drive to add Oregon and California to the new nation. But as is typically the case when territorial expansion occurs quickly, there were political, social and cultural repercussions. These included the Mexican-American War and the displacement and ill-treatment of Native American, Hispanic, and other non-European people living in the regions that were now controlled by the United States. Adding new states to the Union also drove the increasing argument over slavery, raising the question of whether they would allow slavery or not, which eventually led to the Civil War.

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Manifest Destiny, the idea that the United States had the divinely-ordained right to expand all the way to the west coast, had a number of political effects. For one thing, it led to the election of several Democratic presidents, notably James K. Polk, who actively promoted it. It led to the annexation of Texas, which led to the Mexican War, itself driven largely by the idea of manifest destiny. The war resulted in the acquisition of the enormous Mexican Cession, essentially the entire American Southwest, including California. This led to a major indirect political effect of manifest destiny--the political showdown between slave and free states over whether slavery would be allowed in the newly acquired territories. When California applied for admission to the Union, it sparked a major debate over these issues, one which was only momentarily quieted with the Compromise of 1850. Westward expansion was inextricably tied to the ideology of manifest destiny, and it was the persistence of westward expansion that stirred up the lingering issue of slavery. Manifest destiny, or various iterations of it, also contributed to the continued expropriation of Indian lands, which were taken by whites with the assistance of the federal government and the U.S. Army.

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