Was the US justified in going to war with Mexico in 1846?

Answer 1

The answer is no. American presidents John Tyler (term 1841-1845) and James K. Polk (term 1845-1849) wished to extend the US territories to the Pacific coast and consolidate what they saw as the "Manifest Destiny" of the country. US interests had expanded in California and its leaders sought to acquire it by any means necessary. The American settlers in Texas had already split off from Mexico and established a republic since 1836. Its annexation as a US state in 1846 led to border conflicts that quickly escalated into war.

Background to the war

When Mexico won its independence from Spain in 1821, the territories it possessed included Mexico, most of Central America (Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica) as well as today's US States of California, Nevada, Utah, Texas and parts of Colorado, Arizona, New Mexico, and Wyoming.

Due to the extremely low population for such territorial extension (estimated at only 12 million in 1824), Mexico relaxed its immigration policies and allowed American settlers to help populate the northern territories. The conditions to settle were simple: 1) to pledge allegiance to Mexico and 2) observe Mexican laws and customs. In 1830, these laws incorporated the banning of slavery. As many American settlers in such territories were slave owners, they looked for a pretext to secede from Mexican control.

In 1835, Mexican President Antonio Lopez de Santa Anna took measures to transform Mexico from a Federal Republic to a Centralist Republic. This move prompted both Yucatan and Texas to secede from Mexico. Santa Anna's government invaded both regions. While Yucatan was regained, Texas defeated Santa Anna and his armies and became a separate republic in 1836. As is the case with today's mainland China and Taiwan, Mexico saw Texas as a rebellious province to be reincorporated at a later time -- preferably by diplomatic means, but by force if necessary. The Mexican government warned the United States that annexation would mean war.

Texas Annexation

By this time, US President John Tyler had learned of California and its riches. In a letter to Tyler, American Plenipotentiary Minister in Mexico, Waddy Thompson, Jr. wrote :

"As to Texas I regard it as of very little value compared with California, the richest, the most beautiful and the healthiest country in the world... with the acquisition of Upper California we should have the same ascendancy on the Pacific... France and England both have had their eyes upon it."

Tyler believed in Manifest Destiny, a term which meant the annexation of all North America into the United States. He didn't believe in Texas but coveted the other territories west of Louisiana, California being the "Crown Jewel". He eventually pushed for annexation of Texas, offering it admission to the Union on March 1, 1845. His successor, President James K. Polk, ratified the admission on December 29 of that year. These moves had much potential to lead to war with Mexico, and ultimately did so.

The War Begins

Faced with the likelihood that Texas would be lost forever, the Mexican government deposed its president and refused to negotiate with US envoy John Slidell, who had been sent to broker a purchase of the lands. When a US patrol was attacked between the Nueces and Rio Grande Rivers, the US declared war on Mexico, on May 13, 1846. But the first major battles had already taken place between May 3 and 9 at Fort Texas and at Brownsville on the Rio Grande.

Answer 2

No. The U.S. embarked itself into a land-grabbing conflict to accommodate slave-owner interests; it however, was expertly disguised as a Manifest Destiny and even today, most Americans consider the Mexican-American War as a God-given necessity, and not the bullying of a more powerful nation against a weaker and less established one. This conflict however, led to an unsustainable balance of power between pro-slave and anti-slave states, and almost meant the destruction of the Union itself. It finally carried to its logical conclusion with the American Civil War.