Americans of the 19th century were always going to do what was in their best interest when it came to expansion, which lead to the dispelling of Native Americans from their homelands to west of the Mississippi. At the time, it was said that the United States would never expand west of the river, and that their country would forever remain east. Thanks for a high birth rate and rising rates of immigration, this thought would not last long, as population soared in the United States in the first half of the 19th century. By 1850, the population had risen to 23 million people, which was a 460% increase on the population in 1800. When you added in the economic depressions of 1819 and 1839, there were plenty of reasons for people to want fresh beginnings on open land, meaning that the emigration westward was imminent.
Westward expansion began in 1803 with Thomas Jefferson initiating the Louisiana Purchase: adding 828,000 square miles which nearly doubled the size of the United States. The expansion of the United States continued with the acquisition of Florida from the Spanish in 1919, and the Texas annexation and application to become a state, which was finalized under John Tyler in 1844. After all the expansion had occurred, it became obvious to every American of every background, class, and political ties that it was inevitable that the United States would need to expand to the Pacific Ocean. The phrase that was coined for this inevitability was “Manifest Destiny”, which first appeared in the Democratic Review in the summer of 1845. The meaning behind it was that the American leaders were getting a sign from God that there was no other option than to pursue westward.
The first action taken under the newly founded destiny was to determine where the Canadian border should be drawn. President James K. Polk coined the slogan “54˚ 40’ or fight!”, meaning that he desired the Oregon territory to reach up the 54th parallel. After recognizing that there were bigger fish to fry with acquiring California, Polk accepted terms that would split Oregon along the 49th parallel.
The real impact of manifest destiny involved the mentality of American citizens. The thought of having land spread across the continent enthralled the citizens, who took on a “win at all costs” mentality. Because of this, the United States entered an all out war with Mexico, due to their ambitions to complete their expansion. With the signing of the Treaty of Guadalupe Hidalgo, which ended the Mexican-American War in 1848, the United States had completed their goal. In the treaty, America gained 525,000 square miles of U.S. territory which compiled what is now California, Arizona, Colorado, New Mexico, Nevada, Utah, and Wyoming. Even though many saw Manifest Destiny as lofty idealism, this idealism played a major role in making what the continental United States is today, but with it, came the obviously torn relationships with both the Native Americans (who were constantly shifted around) and their Mexican neighbors to the South.