Why Was the Treaty of Guadalupe Hidalgo Important?

Important Treaty of Guadalupe Hidalgo

The concept of Manifest Destiny was deeply ingrained in the American psyche in the early to mid-19th century. This movement would directly lead the US to war with Mexico in 1846. The resulting 1848 Treaty of Guadalupe Hidalgo was an important milestone in achieving this “destiny” of sorts for the United States.

The United States had long been interested in extending its borders to the Pacific Ocean. The travels of Lewis and Clark through the newly-purchased Louisiana Territory captivated the minds of Americans, who began dreaming of the vast lands to the west of them.

After Mexico won independence from Spain in 1821, the manifest destiny concept meant the United States and Mexico were on a collision course. At the time, Mexico’s borders extended much further north than they currently do. Several current US states in the American southwest were actually once possessions of Mexico.

President James K. Polk, in office from 1845-1849, was an ardent expansionist. Polk actually centered his presidential campaign around territorial expansion and this was a primary reason for his nomination by the Democratic Party.

In 1846 Polk was finally able to resolve a longstanding dispute with Great Britain over the Oregon Territory. With the northern US boundaries now settled, the US turned its attention to establishing its territorial boundaries to the southwest.

The question over what to do with Texas and the Mexican territories further to the west were next to be addressed. Years of failed negotiations eventually led to the outbreak of the Mexican-American War in 1846.

The Treaty of Guadalupe Hidalgo ended hostilities in 1848 and was an important event in US history.

Background to the Mexican American War

Central to the Mexican-American War was the issue of what to do with Texas. In 1836 Mexico’s northeastern most territory declared its independence during the Texas Revolution and formed its own state called the Republic of Texas following the Battle of the Alamo and important Battle of San Jacinto.

Mexico never recognized Texas as an independent state, merely viewing it as a province in rebellion. Further compounding the issue was that Texas deemed its southern border to be at the Rio Grande, while Mexico declared the more northern Nueces river to be the territory’s southern border.1

This led to a tricky diplomatic situation for Mexico’s neighbors and other countries. The United States, France, United Kingdom, and several other nations officially recognized Texas as an independent republic despite Mexican protests.

The majority of Texas’ population was comprised of American settlers who ultimately wished to be annexed into the United States.

Texas annexaion map
Map of prewar borders, including Texas’ claims via Wikimedia

The political situation at the time was untenable as slavery was an extremely divisive issue. Texas was a slave state and in general, if Congress added a slave state to the Union, a corresponding free state also needed to be added.

Under President James K. Polk, the United States officially agreed to annex the Republic of Texas in 1845. The US admitted Texas into the Union in December 1845, with the free state of Wisconsin added just two years later.

News of the Texas annexation left Mexico furious. In addition, the southern border dispute had been left unresolved with Mexico still believing the border to be at the Nueces river, while the United States believed the border to be at the Rio Grande.

In a last ditch effort to acquire territory peacefully, Polk sent special envoy John Slidell (known for his later role in the 1861 Trent Affair) to Mexico in November 1845 to attempt to purchase the territories of New Mexico and Alta California.

When Mexico refused the offer, Polk sent troops to the disputed territory near the Rio Grande hoping the presence of those troops would provoke Mexico to attack.

Polk received his wish in April 1846, when Mexican troops attacked US troops near the Rio Grande in the Thornton Affair. Congress would declare war on Mexico in May 1846.

What did the Treaty of Guadalupe Hidalgo Accomplish?

The Treaty of Guadalupe Hidalgo accomplished a peaceful conclusion to the Mexican American War in 1848. The terms resulted in the Mexican Cession whereby the United States obtained a huge swath of territory.

Polk initially believed the war would take no more than a few months to conclude. The Americans scored early victories on the battlefield and successfully occupied a majority of the northernmost Mexican territories.

However, Mexico proved resilient and unwilling to capitulate or give in to the American peace terms. Polk thus hoped to “conquer a peace,” or use the superior US military advantage to strong-arm Mexico into giving in to US demands.2

By September 1847 the United States occupied Mexico’s capital city. In order to expel the invaders, Mexico would need to agree to a peace treaty. Peace terms would not be straightforward, given Mexico’s weak centralized government and multiple competing factions, each with their own priorities.

Battle of Monterrey
Depiction of the Battle of Monterrey via LOC

Chief Clerk of the State Department Nicholas Trist was sent to negotiate terms for the United States. The United States aimed to secure the exact same territories of New Mexico and Alta California that Slidell had attempted to purchase just two years earlier. This time it came with the cost of thousands of American lives.

Trist failed to make progress and thus President Polk recalled him after months of negotiations in November 1847.

As he was about to leave the country, the Mexican government finally committed three commissioners to seriously negotiate peace terms. Sensing an opportunity he could not pass up, Trist immediately resumed negotiations, despite his lack of authority to do so.

On February 2, 1848 Trist signed the Treaty of Guadalupe Hidalgo on behalf of the United States, officially bringing an end to the Mexican-American War.

Trist forwarded on the treaty to Polk by the fastest means available. While Polk was outraged that Trist negotiated and signed the important treaty on behalf of the US without authorization, the Treaty of Guadalupe Hidalgo contained everything he wanted.

The Senate ratified the Treaty of Guadalupe Hidalgo on March 10, 1848 after modifying one article (Article IX) and eliminating another (Article X).

What did the Treaty of Guadalupe Hidalgo Promise?

The Treaty of Guadalupe Hidalgo promised that Mexico would cede its northernmost territories, which combined to account for about 55% of its prewar territory.

These territories included New Mexico, Alta California (which includes modern-day California, Arizona, Nevada, Utah, and parts of Colorado, Wyoming, and Kansas) as well as extending Texas’ southern boundary to the Rio Grande.

Historians also refer to this vast amount of territory as the “Mexican Cession.” In return for all the territory, the US granted Mexico the sum of $15 million, to be paid in annual installments of $3 million upon ratification of the treaty.

Terms of the 1848 Treaty of Guadalupe Hidalgo important chart

The Treaty of Guadalupe Hidalgo also promised and guaranteed certain citizenship and property rights to Mexican citizens living in the newly-acquired US territories.3

All Mexican citizens living in the new US territories were given the option to become US citizens, or to remain Mexican citizens and return to Mexico. The treaty stipulated that Mexicans needed inform the US government within one year otherwise by default they would become US citizens.

Nearly 90% of the Mexican population in the new US territories chose to remain and become US citizens. This guarantee of citizenship also came with a promise that the Mexicans would retain their lands and property ownership.

While the treaty granted Mexicans full citizenship in the territories, white settlers from westward expansion soon outnumbered them. These original inhabitants often faced racial discrimination and illegal seizure of property.

Despite the clear terms of the Treaty of Guadalupe Hidalgo, settlers and lawmakers did not honor many Mexican-American citizens’ property rights. To this day there are efforts to address this injustice via Congressional legislation.3

Why was the Treaty of Guadalupe Hidalgo Important?

The Treaty of Guadalupe Hidalgo was important for several reasons:

  1. The US obtained a large amount of territory via the Mexican Cession
  2. The US realized its ambition of Manifest Destiny by acquiring territory to the Pacific Ocean
  3. Reignited the issue of slavery in US politics via the Wilmot Proviso

The United States would not stop there with its expansionist tendencies. The years following would see further expansion with the Gadsden Purchase, purchase of Alaska, and annexation of Hawaii, among other future territorial acquisitions.

Treaty of Guadalupe Hidalgo map
The Mexican Cession completed Manifest Destiny in the US via census.gov

These acquired territories would soon provide enormous strategic, economic, and commercial benefits to the United States. In fact, just a week before the Treaty of Guadalupe Hidalgo was signed, gold was found in California that would spark a massive population boom and send scores of settlers west along the Oregon Trail.

The new Pacific coast ports would also help the US to establish more trade routes with East Asian markets such as China and eventually Japan.

The Treaty of Guadalupe Hidalgo was also important in that it reignited the political arena on the issue of slavery. In prior decades during the Jacksonian Era, politicians from both parties tried to avoid the topic of slavery and focus on other issues.

The new territories brought fierce debate regarding the institution of slavery and whether the important Missouri Compromise would continue to apply. The Wilmot Proviso sought to completely ban slaves in the acquired territories though never became law.

The question of slavery in the territories would feature far more often in the lead up to the Civil War. The 1858 Lincoln-Douglas Debates, the infamous Dred Scott Decision, and John Brown’s raid on Harper’s Ferry each had slavery at their roots.

While the Mexican-American War cost the United States many lives, the Treaty of Guadalupe Hidalgo played an important role in the growth of the nation.


To learn more about US history, check out this timeline of the history of the United States.


1) Brent, Robert A. “Nicholas P. Trist and the Treaty of Guadalupe Hidalgo.” The Southwestern Historical Quarterly, vol. 57, no. 4, 1954, pp. 454–74, http://www.jstor.org/stable/30240740.

2) Reeves, Jesse S. “The Treaty of Guadalupe-Hidalgo.” The American Historical Review, vol. 10, no. 2, 1905, pp. 309–24, https://doi.org/10.2307/1834723.

3) Martínez, George A. “Dispute Resolution and the Treaty of Guadalupe Hidalgo: PARALLELS AND POSSIBLE LESSONS FOR DISPUTE RESOLUTION UNDER NAFTA.” Bilingual Review / La Revista Bilingüe, vol. 25, no. 1, 2000, pp. 39–61, http://www.jstor.org/stable/25745690.

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