History of the War



Timeline of Major Events

Influential Characters

The Main Battles

Outcome of the War

The Opposing Viewpoints

Note Page

Image Sources



From 1846 to 1848, U.S. and Mexican troops fought against one another in the Mexican-American War.  Ultimately, it was a battle for land where Mexico was fighting to keep what they thought was their property and the U.S. desired to retain the disputed land of Texas and obtain more of Mexico’s northern lands.  Thus, the roots of this war long precede the fighting that began on April 25th, 1846. 


"After reiterated menaces, Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American Soil. She has proclaimed that hostilities have commenced, and that the two nations are at war."(2)
U.S. President James K. Polk
   May 11, 1846

Collage representing scenes in the Mexican-American War

Courtesy of the TV Digital Archives
Linda Arnold



Two Main Causes of the Mexican American War

  1. The Mexican American War was mainly driven by the idea of “Manifest Destiny”; the belief that the U.S had a God-given right to occupy and civilize the whole continent. As increasingly large number of Americans migrated towards the west in search of land, the fact that most of those areas already had people living in them was ignored. Instead, an attitude and belief that democratic English-speaking America would do a better job of running the lands than the Native Americans or Spanish-speaking Catholic Mexicans prevailed. President Polk shared and led the vision of Manifest Destiny, and did offer to buy much of the southwest land from Mexico. However the Mexican government refused the offer, and an unyeilding desire to populate those southwestern lands caused tensions to continue to rise. (3)

  2. The second major cause of the Mexican American War actually started off with the Texas War of Independence and the subsequent inclusion of that area into the United States. During the 1830s, Mexico needed settlers in the under populated northern parts of the country and therefore allowed U.S. citizens to come and live in the Texas area as long as they took an oath of allegiance to Mexico and coverted to Catholicism. Thousands of Americans accepted the invitation and migrated to the Mexican province of Texas. However, not long after, many of the new “Texicans” or “Texians” were not satisfied with the way the Mexican government tried to run the province. So in 1835, the Texas Revolution began as both Mexicans and Americans living in Texas fought for independence from the Mexican government. Sam Houston led the "Texians" in battle against Mexican President Santa Anna and his troops. A final victory resulted in the capture of Santa Anna, who was forced to sign the Treaty of Velasco, granting Texas its independence. (4)


Still, the Republic of Texas and Mexico continued to have battles; many Americans in the U.S openly sympathized with the U.S born Texans in this conflict leading the Americans in developing a very negative stereotype against the Mexicans and the government. Partly due to the continued hostilities with Mexico, Texas decided to unite with the United States and, by 1845, U.S Congress had approved this union.(5) This, of course, left Mexico unhappy with the United States, and the undefined border and contested land developed into a major issue. Both nations sent troops to compete for and claim the land betwen the rivers that they both claimed as theirs. Mexico claimed the Nueces River as its northeastern border, while the U.S. claimed the Rio Grande River, and the day that both troops met at the Rio Grande and the Mexican army opened fire, on April 25, 1846, the Mexican American War began.