MEXICAN-AMERICAN WAR
1846 - 1848
Picture: U.S. General Winfield Scott and his troops
entering Mexico City on September 14, 1847
 

The Mexican-American War is also called the Mexican War or Guerra de 1847.

This war was fought April 25, 1846 - February 2, 1848. The Americans won. Mexico lost big.

Involved was Antonio López de Santa Anna, who lost California, Arizona, and New Mexico for his country.

WHAT STARTED THE WAR?
Mexico viewed the Nueces River as their boundary. The Americans rather saw the Rio Grande as their boundary.

When American General Zachary Taylor crossed the Nueces River and stationed his troops at Point Isabel, Mexican General Mariano Arista and his troops crossed the Rio Grande. They ran into each other for the first time on April 25, 1846.

MEXICO CLAIMED THE NUECES RIVER, THE
UNITED STATES THE RIO GRANDE AS THEIR BOUNDARY
CLICK MAP TO ENLARGE
 

WHAT ENDED THE WAR?
The Treaty of Guadalupe Hidalgo ended the war. The United States won.

THE BATTLES OF THE MEXICAN-AMERICAN WAR
Among others, the battles of the Mexican-American war were as follows:

May 8, 1846 - Battle of Palo Alto
May 9, 1846 - Battle of Resaca de la Palma
February 22 - 23, 1847 - Battle of Buena Vista
April 18, 1847 - Battle of Cerro Gordo
 

CLICK MAP TO ENLARGE

TRIVIA
The United States declared war on Mexico on May 13, 1846. The reason? Mexican troops stationed at Matamoros targeted Fort Brown. President James Knox Polk officially recognized this as an invasion of American soil.

Here is a map of the campaign routes

MEXICAN AMERICAN WAR
Click map to enlarge

And here's a map of the US Battle Sites

United States 1689 - 1945 Battle Sites
Click Map to enlarge

The following is quoted from the Atlas of Texas, Copyright 1976 Board of Regents, The University of Texas System. Used by permission of the University of Texas Libraries, The University of Texas at Austin.

In July 1845 Texas formally accepted an American proposal to be annexed to the United States. Already strained relations between the United States and Mexico rapidly worsened. President James K. Polk ordered General Zachary Taylor and his troops to Corpus Christi. In March 1846, under instructions, Taylor took up positions on the Rio Grande. On April 26 an American squadron of dragoons surrounded by Mexicans and unable to fight its way out surrendered. Several Americans lost their lives in the defeat.

On May 8 the Mexicans intercepted Taylor at Palo Alto but were driven back. The next day Mexicans again gave way in battle at Resaca de la Palma. In June Taylor began a march toward Monterrey, taking that city on September 25. Two months later the Americans took Saltillo and with little effort filed into Tampico.

Santa Anna now took the field against the American forces in northern Mexico, finally engaging the Americans at Buena Vista in February. Upon learning of the Mexican's design, General John E. Wool marched from San Antonio to join Taylor's forces, abandoning his prior plans to take Chihuahua. After extremely bitter fighting Santa Anna pulled out his army, leaving Taylor in control of northern Mexico.

While Taylor pursued the enemy, Colonel Stephen W. Kearny took the "Army of the West" into New Mexico, capturing Santa Fe on August 16, 1846. Kearny then divided his forces, taking part to California and sending the remainder under Alexander W. Doniphan against Chihuahua. After General Winfield Scott captured Mexico City the two countries finally reached a settlement.

Source: Maps adapted from The West Point Atlas of American Wars, Volume 1, Frederick A. Praeger, 1959. 
 

Check the costs of major US wars in comparison.