American Imperialism and The Mexican War
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As western poulation increased so did the advocation of Manifest Destiny. People from this are had a growing desire to annex new territories, putting pressure on the government to acquire more lands like Texas and Oregon. This urge for American Imperialism played a huge role in the upcoming 1844 election, in which expansionist James K. Polk defeated Martin Van Burenfor the Democratic party's nomination, and then indecisive Whig Henry Clay for the presidency 170 electoral votes to 100. Quickly, Polk set out to achieve these imperialist goals, the first of which John Tyler facilitated by gaining congressional approval for the annexation of Texas in February 1845. By December of that year Texas was a state, and Polk was making large strides to resolve the Oregon question with England, offering to establish the United States-Canda border on the 49th parallel. After initial rejection by England and the American institution of the slogan "Fifty-four forty or fight", England and the US settled for the 49th parallel.

American actions in 1845 would lay the foundation for the Mexican War. Soon after Texas was admitted into the US, Mexico would end all diplomacy with the American people, and a dispute over the Texas-Mexico border would come as a result. Texans would claim the Rio Grande as thier western and southern border, while Mexico was adament in their belief that the Texas-Mexico border was, and always had been the Nueces River north of the Rio Grande. The southwest also faced strife in New Mexico, where the Santa Fe trading center was located, and by the 1840's, a primarily American territory. Epansionist feelings began to spread to Mexican California too, as merchants, pioneers, and other fronteirsman began to gravitate farther west. It didn't take long for President Polk to fix his crosshairs on to New Mexico and California. In the summer of 1845 Polk sent American troops led by General Zachary Taylor to Texas in case of a possible Mexican invasion. In addition to those orders, Polk issued secret instructions to the commander of the Pacific naval squadron to seize California points as orecaution to a Mexican declaration of war.

Iexternal image mex-war-map.jpgn an attempt to avoid a war with Mexico, Polk sent a special minister, John Slidell, to settle things in a more diplomatic matter ($50 million buy out). On January 13, 1846, after the failure of the Slidell Mission, Polk ordered Taylor and his troops to cross the Nueces River and proceed to the Rio Grande. After months of Mexican refusal to fight, it is said (by disputed American accounts) that a group of Mexican soldiers initiated war by attacking American troops stationed around the Rio Grande. After this, Polk claimed war existed with the Mexicans, and on May 13, 1846, the overwhelming majority of Congress voted yes to the declaration of war against Mexico. This war did not go without opposistion, as many Whigs claimed that Polk's previous actions were all to facilitate his hopes for war; others believed that war with Mexico was draining resources and attention from the more important issues of the Pacific Northwest.

In September of 1846 Polk ordered Taylor to seize Monterrey. Taylor succeede in this venture, but let Mexican troops evacuate without pursexternal image bearflag.jpguit. This action plated seeds of doubt in Polk's mind about Taylor's ability as a general, wondering if he was aggressive enough to carry on the planned advances against Mexico City, and also fearing that, if successful, Taylor could stand as a political challenge and rival to him. Polk still persisted to order offensives, now in New Mexico and California. These offensives led to Colonel Stephen W. Kearney'scapture of Santa Fe in the summer of 1846. Kearney then joined the navy and American settlers under John C. Fremont, eventually leading them to victory in their so-called Bear Flag Revolution, and the the complete conquest of California by autumn of the same year. America now controlled both territories they wanted, but the Mexican government refused to admit defeat. Mexican stubborness caused Polk and General Winfield Scott to launch a new campaign, one that would force Mexican concession. Scott assembled a 14,000 man army at Tampico and proceded to advance 260 miles along the Mexican National Highway, all the way to their capital, Mexico City. Keeping American casualties at a minimum, and never losing a battle along the march, Scott's men forced a new Mexican government to surrender peacefully, and prepare for negotiations.external image treatyGuadHidLg.jpg

On February 2, 1848 Polk's negotiator Nicolas Trist reached an agreement with the Mexican government. The agreed Treaty of Guadalupe Hidalgo ceded California and New Mexico to the United States, and acknowledged the legitimacy of the Rio Grande border of Texas. In return, the US promised to assume any financial claims its citizens had against Mexico, as well as payment of $15 million to the Mexican people. Although Trist's agreement did not fulfill all of the expansionist dreams (acquiring all of Mexico), Polk submitted it to the Senate, which approved the treaty with a vote of 38 to 14. The war did not end as quickly as orignally anticipated, but it was finally over and with its end came a series of issues that would highlight the sectional controversies of the time and define America for years to come.

A Survey: American History by Alan Brinkley, twelfth edition