Effects of the Mexican-American War


The Mexican-American War (1846-1848) was caused by many factors.

Going back to 1836, one of the reasons was the Treaty  of Velasco.  The secret treaty had called for recognition of the Rio Grande as the border, and the release of Santa Anna.  Since Santa Anna was not released immediately, the border was never officially established.

The Rio Grande border was another cause of the war.  Mexico believed that the border was actually the Nueces River, about 200 miles north of the Rio Grande.

Texans, and the US claimed the Rio Grande as the border.  The disputed  land in between the two rivers is a rich farmland.

The final cause was Texas joining the United States in 1845.  Mexico became alarmed that the US was out to grab all the land it could, and that Mexico would be it's next target.

Fighting in the Mexican-American War lasted only two years; from 1846 to 1848.  The battles ranged from the Rio Grande, down to Mexico City; from New Mexico to California.

All battles were won by Texan, or US forces.  In fact, most US Army deaths were caused by disease and not battles!

Patient being treated for yellow fever

The National Palace in Mexico City

The war ended when the US Army captured Mexico City.  In fact, the US flag flew over the Mexican National Palace!

Once the war was over, then the peace process could begin.  First though, they needed to write and sign a treaty.

US Wins Mexican-American War

Land gained by the Mexican Cession

The treaty that ended the war was called the Treaty of Guadalupe Hidalgo.  Since the US won, they got to set the terms (conditions).

Mexico agreed to the treaty, and the war was officially over on 2/2/1848.


  • Mexican Cession  - Mexico sells land to the US.  Fro million, US receives California, New Mexico, Arizona, Utah, Colorado, and part of Wyoming.
  • All Mexicans living in this area would be allowed to become US citizens.


The war affected the US, specifically Texas, and Mexico.

For Mexico, there was loss of life, economic ruin, and huge damage to property.

For the US, they gained huge new pieces of land.  However the fight over what to do with it took center stage.  Would these new lands be Slave states of Free states?

Tejanos  in Texas were viewed as enemies, before & during the war.  After the war, they were discriminated against.  Many Tejanos lost their property and their homes.

Texas saw an increase in population.  The European population rose due to conflicts in many countries.  More slaves came to Texas with their owners.

The Mexican-American War (1846-1848) was a brief war that had lasting consequences.  Through it, the US was able to complete it's Manifest Destiny  and gain land coast-to-coast.

Texas' border was finally secured between it and Mexico.  No longer would there be any question over the land.

From this point on, the US was a superpower!