Mexican-American War and the Treaty of Guadalupe-Hidalgo

The Mexican-American War and the Treaty of Guadalupe Hidalgo

So far from God, so close to the United States – Old Mexican Saying

On September 14, 1847 the Mexican flag was not flying over the Mexican capital. Instead, Mexico’s neighbor to the north had captured the country. How and why did the United States defeat Mexico in the Mexican-American War? To the victors went what spoils? This essay will answer these questions in a nutshell.

Throughout the 19th Century, the United States was increasing in power and population while Mexico was stuck in chronic “political unrest, civil conflicts, depleted treasuries, [and] separatist movements” (Oscar J. Martinez, Troublesome Border [Tucson: the University of Arizona Press, 1988], 51). The U.S. was also heavily influenced by Manifest Destiny—the idea that the U.S. had the natural right to rule North America from coast to coast. Consequently, various presidential administrations in the 1820s and 30s sought to purchase land from Mexico, with no avail.

In 1835, Texas battled and gained independence from Mexico; Texas was a sovereign country for the next decade (the Lone Star Republic). In the Treaty of Velasco, the Texas-Mexico border was established along the Rio Grande. Mexican President Antonio Lopez de Santa Anna (pronounced “Santana”) signed the treaty but the problem lied in the fact that the Mexican Congress did not ratify it, nor did Mexican presidents after Santa Anna acknowledge Texas’ independence.

Texas was annexed by the United States in 1845. Mexico claimed the international border to be the Nuecos River, while the U.S. claimed the border to be at the Rio Grande. The Nuecos River runs roughly parallel to the Rio Grande about fifty to one-hundred miles northeast (the Texas side) of it. Therefore, by claiming their respective river boundaries, both countries were trying to expand their territory. When the Mexican army crossed the Rio Grande and skirmished with U.S. soldiers, President Polk declared that America had been invaded and American blood had been shed. These words meant one thing: war.

mexican american war battle scene
Mexican-American War battle scene

Library of Congress


The Mexican–American War was an embarrassment for Mexico and a goldmine for the United States, literally. Within days, the important port of Veracruz was blockaded by the U.S. navy. The U.S. army fought their way overland into Mexico from California, Texas, and eventually from Veracruz straight to the capitol. Mexico’s Santa Anna, back in power again, sent a peace treaty to Washington in early 1847, but his terms were not approved. Later on that year, with U.S. troops just outside Mexico City, peace talks occurred. When Mexico would not admit defeat and offer up territory, American troops invaded the capital city and quickly took control. Santa Anna resigned as president and fled central Mexico in defeat. The United States now occupied the Mexican capital, thus the U.S. occupied Mexico, now what could it take?

It was a long negotiation process that ultimately led to the Treaty of Guadalupe-Hidalgo on February 2, 1848. President Polk sent “Peace Ambassador” Nicholas Trist to central Mexico in order to set the terms of the Treaty. On a note of interest, Trist was recalled by Polk but disobeyed orders to go back to Washington; he was the only American to sign the Treaty of Guadalupe-Hidalgo. If Trist would have left for Washington like he was ordered to do, the treaty would probably never have happened. With this Treaty, the American Southwest as we know it today officially came under U.S. control and Mexico lost half of its country. The treaty established the Texas-Mexican border along the Rio Grande; fifteen years later it would be the same river that led to the Chamizal dispute between Mexico and the United States. It was agreed that a group of surveyors from each country, working together, would set out to map the new 2,000-mile long border.

Just weeks after the treaty was signed, gold was discovered in California (California was known for a long time as El Dorado, which means “the land of gold” in Spanish), leading to the largest gold rush in the history of the United States. But unfortunately for Mexico, El Dorado was not part of Mexico anymore.

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Last updated: February 24, 2015

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