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Causes of the Mexican War

Causes of the Mexican War
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Effects of the Mexican War


When referring to the Mexican War, President Polk once said, "Well may the boldest fear and the wisest tremble when incurring responsibilities on which may depend our country's peace and prosperity”(Martin, Kelly) .It was with this pompous attitude that our nation entered the Mexican-American war in 1846. While there were many events that led our nation into war, the causes most responsible for the outbreak of the war include the idea of Manifest Destiny, the actions of President Polk, and the annexation of Texas.

            Manifest Destiny was a phrase used by those in the 1840’s to explain the expansion of the United States. In many ways, Manifest Destiny pushed our nation towards the Mexican War. While it was only a concept, it gave Americans the confidence and a justifiable reason to conquer and acquire new lands. “It is dangerous to underestimate the power of an idea. Especially one which captures the imagination of a people. Manifest Destiny was such an idea. To extend American democracy to the rest of the continent was to place a mantle of legitimacy on what was essentially an insatiable ambition for land” (Quiroga, Miguel). Manifest Destiny gave the United States a great desire to expand west ward, claiming that Americans occupation of new lands was a right granted to them by God. As expressed by Roger Lee, consideration was not taken for those whose land was taken over.

“The fact that most of those areas already had people living upon them was usually ignored, with the attitude that democratic English-speaking America, with its high ideals and Protestant Christian ethics, would do a better job of running things than the Native Americans or Spanish-speaking Catholic Mexicans.” (Lee, Roger)

While Manifest Destiny did not call for violence, it provided Americans with the ambition and confidence they needed to enter the Mexican War. Therefore America’s desire for expansion was one of the biggest causes of the United State’s war with Mexico.

            President Polk also played a large role in the outbreak of the Mexican War. Many claim that his desire’s for westward expansion caused him to entice Mexico into the war. Before the war had began, Mexico and the United States had different beliefs on where the borders between the two nations lied. While American’s believed the border existed at the Rio Grande, the Mexican government insisted that its countries northern border existed at the Neuces River. ( Pike, John ).  When Polk ordered American troops into the region that was being disputed, many felt that this was an act of aggression that was unnecessary. “A Delaware Senator declared that ordering Taylor to the Rio Grande was "as much an act of aggression on our part as is a man's pointing a pistol at another's breast." “ (Mintz, Steven). Polk’s aggression towards the United States newly independent neighbor, Mexico, was one event that provoked the war between the two nations.

            The Annexation of Texas, was the most obvious cause of the Mexican War.  After becoming independent from Mexico, Texas’ induction as an American State helped to quickly destroy the deteriorating relationship between Mexico and the United States. Texas had just fought a bloody war for its independence with Mexico. The frontier’s savage fighting caused Americans to negatively stereotype both the Mexican people and its government. While the Treaty of Velasco had given Texas its independence in 1836, Mexican’s claimed that the document was illegitimate. And the hostile relationship between Texas and Mexico pushed Texas towards joining the United States and on July 4, 1845, Congress approved Texas’ annexation (Lee, Roger). The vote to annex Texas, caused great anger in Mexico as the American ambassador was expelled and Mexico cut off all diplomatic ties with the United States (Mintz, Steven). The annexation of Texas placed a great deal of hostility between the United States and Mexico and was one of the causes of the Mexican War.

            When determining what it was responsible for the war between Mexico and the United States in the late 1840’s you could find many possible answers. Instead of one event, instead there are many causes which all added together total a sum of great enough hostility that two nations would feel it necessary to fight against one another. Therefore it was the combination of the ideas of Manifest Destiny, the provoking ways of President Polk, and the annexation of Texas that caused the Mexican War. One not being more important that the other, but merely playing their role in the intensifying bitterness that would eventually lead to the outbreak of war.


Works Cited

Kelly, Martin. “ Quotes from James K. Polk.” 2005. About. 4 June. 2005.

Lee, Roger. “The Mexican – American War.” 23 May. 2005. The History Guy. 6 June. 2005. <>

Mintz, Steven. “ Westward Expansion: Mexican War.” 7 June. 2005. Digital History. 7 June. 2005.  <>

Pike, John. “Mexican War.” 27 April. 2005. Global Security Organization. 7 June. 2005.


Quiroga, Miguel. “The Power of an Idea.” PBS Online. 6 June. 2005. <>

President James K. Polk