The Mexican American War  -- why it started.


Did the U.S. used subterfuge to create a war and thus seize territory? Or did Mexico cause the War by hostile actions that forced a U.S. response? Excerpts below give an outline of the issue, including the fact that Mexico declared war on the U.S. before the border dispute, as soon as Texas joined the U.S. It seems to be that the U.S. did not have to pursue hostilities with Mexico after securing the border. It is not as if the U.S. was threatened by an invasion. Henry Clay, Daniel Webster and Abraham Lincoln opposed the war.


From the Brazoria County Museum (Texas) website.


Fifteen years before the Civil War, the United States fought a war against Mexico that added a half million square miles of territory to the United States. The annexation of Texas in 1845 gaverise to the U.S. - Mexican war of 1846 - 1848. It was a controversial war that heightened the conflict between North and South. The underlying cause was the movement of Americans into the Far West. As Americans moved west, their land claims conflicted with those of Mexico.

Following the battle of San Jacinto, which ended the Texas war for independence from Mexico, Mexican General and President Santa Anna had signed the "Treaties of Velasco," (in the town of Velasco, at the mouth of the Brazos River). In the eyes of Texans, those treaties recognized the new Republic's independence from Mexico and established the Rio Grande River as the western boundary of their new country. When the U.S. later annexed Texas, it too, claimed that boundary.

Mexico, on the other hand, insisted that the boundary was the Nueces River. In spite of the fact that Santa Anna had signed the treaties, Mexico refused to recognize them. She later warned the United States that annexation of Texas would be seen as a declaration of war and did indeed, issue that declaration when Texas was annexed in 1845. Mexico did not, however, provoke war. The United States did.

Antonio L๓pez de Santa Anna


The map shows the boundaries of Texas as understood by Texans in 1836 and by the United States when it annexed Texas in 1845.

Now in the most aggressively expansionist phase of its history--commonly known as the period of "Manifest Destiny"--the United States fully intended to secure the region between the Nueces and Rio Grande for itself.

It did not intend to stop there. President Polk and the Democratic Party had designs on Mexican territory all the way to the Pacific.

Frustrated in his efforts to purchase Mexican territory, Polk dispatched General Zachary Taylor and U.S. Army troops to the Rio Grande. When informed of a skirmish between U.S. and Mexican forces on the northern bank of the Rio Grande--Polk sent a message to Congress that "Mexico has passed the boundary of the United States and shed American blood on American soil." Congress declared war against Mexico.

Zachary Taylor (1784-1850)

It was, as noted, a controversial war. Supporters, primarily southerners, argued that the United States was destined to expand westward. They blamed Mexico for the hostilities because it had severed relations with the United States and threatened war.

Two of American's most prominent politicians, Henry Clay and Daniel Webster denounced the war as a pretext for stealing land and as an unnecessary and offensive aggression.

Abraham Lincoln, a young congressman from Illinois, labeled it an immoral war, blatantly proslavery and a threat to the nation's republican values.

Northern opposition leaders denounced the war as an immoral land grab against a weak neighbor. The critics claimed that President Polk deliberately provoked Mexico into war by ordering American troops into disputed territory. They also argued that the conflict was an expansionist plan by southern slave owners intent on acquiring more land for cotton cultivation and more slave states.

Mexico eventually sued for peace and "sold" the northern half of its country to the United States for $15 million. With Polk's 1844 settlement of the Oregon boundary dispute with Great Britain at the 49th parallel, the 1848 Treaty of Guadalupe Hidalgo, and the $10 million Gadsden Purchase in 1853 (see map, next panel), the United States consolidated its continental empire to the Pacific.


From a U.S. Whitehouse website

Acquisition of California proved far more difficult. Polk sent an envoy to offer Mexico up to $20,000,000, plus settlement of damage claims owed to Americans, in return for California and the New Mexico country. Since no Mexican leader could cede half his country and still stay in power, Polk's envoy was not received. To bring pressure, Polk sent Gen. Zachary Taylor to the disputed area on the Rio Grande.

To Mexican troops this was aggression, and they attacked Taylor's forces.

Congress declared war and, despite much Northern opposition, supported the military operations.











David Saville Muzzey's popular 1911 text "American History" explained the Mexican War to school children of the early twentieth century, told why the United States seized California in 1846, and how the U.S. ended the Texas-Mexico border dispute. The Treaty of Guadalupe-Hidalgo, which officially ended the war, was signed in 1848, just nine days after gold was discovered at Sutter's Mill. Dr. Muzzey's text also gave great insight into contemporary American thinking about "Manifest Destiny." This text, and its revised editions, was still in classroom use as late as the 1940's.

The Mexican War
by David Saville Muzzey, Ph.D.
Barnard College, Columbia University, New York

Mexico refuses to recognize the Annexation of Texas.

The annexation of Texas was a perfectly fair transaction. For nine years, since the victory of San Jacinto in 1836, Texas had been an independent republic, whose reconquest Mexico had not the slightest chance of effecting. President James L. PolkIn fact, at the very moment of annexation, the Mexican government, at the suggestion of England, had agreed to recognize the independence of Texas, on condition that the republic should not join itself to the United States. We were not taking Mexican territory, then, in annexing Texas. The new state had come into the Union claiming the Rio Grande as her southern and western boundary. By the terms of annexation all boundary disputes with Mexico were referred by Texas to the government of the United States. President Polk sent John Slidell of Louisiana to Mexico in the autumn of 1845 to adjust any differences over the Texan claims. But though Slidell labored for months to get a hearing, two successive presidents of revolution-torn Mexico refused to recognize him, and he was dismissed from the country in August, 1846.

Taylor attacked on the Rio Grande.

The massing of Mexican troops on the southern bank of the Rio Grande, coupled with the refusal of the Mexican government to receive Slidell, led President Polk to order General Zachary Taylor to move to the borders. Taylor marched to the Rio Grande and fortified a position on the northern bank. The Mexican and the American troops were thus facing each other across the river. When Taylor refused to retreat to the Nueces, the Mexican commander

crossed the Rio Grande, ambushed a scouting force of 63 Americans, and killed or wounded 16 of them (April 24, 1846).

The United States accepts War with Mexico.

When the news of the attack reached Washington early in May, Polk sent a special message to Congress, concluding with these words:

"We have tried every effort at reconciliation...But now, after reiterated menaces, Mexico has passed the boundary of the United States [the Rio Grande], 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. As war exists, and, notwithstanding all our efforts to avoid it, exists by the act of Mexico herself, we are called upon by every consideration of duty and patriotism to vindicate with decision the honor, the rights, and the interests of our country."






From: the History Guy website

The war between the United States and Mexico had two basic causes. First, the desire of the U.S. to expand across the North American continent to the Pacific Ocean caused conflict with all of its neighbors; from the British in Canada and Oregon to the Mexicans in the southwest and, of course, with the Native Americans. Ever since President Jefferson's acquisition of the Louisiana Territory in 1803, Americans migrated westward in ever increasing numbers, often into lands not belonging to the United States. By the time President Polk came to office in 1845, an idea called "Manifest Destiny" had taken root among the American people, and the new occupant of the White House was a firm believer in the idea of expansion. The belief that the U.S. basically had a God-given right to occupy and "civilize" the whole continent gained favor as more and more Americans settled the western lands. The fact that most of those areas already had people living upon them was usually ignored, with the attitude that democratic English-speaking America, with its high ideals and Protestant Christian ethics, would do a better job of running things than the Native Americans or Spanish-speaking Catholic Mexicans. Manifest Destiny did not necessarily call for violent expansion. In both 1835 and 1845, the United States offered to purchase California from Mexico, for $5 million and $25 million, respectively. The Mexican government refused the opportunity to sell half of its country to Mexico's most dangerous neighbor.

The second basic cause of the war was the Texas War of Independence and the subsequent annexation of that area to the United States. Not all American westward migration was unwelcome. In the 1820's and 1830's, Mexico, newly independent from Spain, needed settlers in the under-populated northern parts of the country. An invitation was issued for people who would take an oath of allegiance to Mexico and convert to Catholicism, the state religion. Thousands of Americans took up the offer and moved, often with slaves, to the Mexican province of Texas. Soon however, many of the new "Texicans" or "Texians" were unhappy with the way the government in Mexico City tried to run the province. In 1835, Texas revolted, and after several bloody battles, the Mexican President, Santa Anna, was forced to sign the Treaty of Velasco in 1836 . This treaty gave Texas its independence, but many Mexicans refused to accept the legality of this document, as Santa Anna was a prisoner of the Texans at the time. The Republic of Texas and Mexico continued to engage in border fights and many people in the United States openly sympathized with the U.S.-born Texans in this conflict. As a result of the savage frontier fighting, the American public developed a very negative stereotype against the Mexican people and government. Partly due to the continued hostilities with Mexico, Texas decided to join with the United States, and on July 4, 1845, the annexation gained approval from the U.S. Congress.

Mexico of course did not like the idea of its breakaway province becoming an American state, and the undefined and contested border now became a major international issue. Texas, and now the United States, claimed the border at the Rio Grande River. Mexico claimed territory as far north as the Nueces River. Both nations sent troops to enforce the competing claims, and a tense standoff ensued. On April 25, 1846, a clash occurred between Mexican and American troops on soil claimed by both countries. The war had begun.


From the Columbia Encyclopedia, 6th edition


   Another major factor was the American ambition, publicly stated by President Polk, of acquiring California, upon which it was believed France and Great Britain were casting covetous eyes. Despite the rupture of diplomatic relations between Mexico and the United States that followed congressional consent to the admission of Texas into the Union, President Polk sent John Slidell to Mexico to negotiate a settlement. Slidell was authorized to purchase California and New Mexico, part of which was claimed by Texas, and to offer the U.S. government’s assumption of liability for the claims of U.S. citizens in return for boundary adjustments.

   When Mexico declined to negotiate, the United States prepared to take by force what it could not achieve by diplomacy. The war was heartily supported by the outright imperialists and by those who wished slave-holding territory extended. The settlement of the Oregon boundary dispute (June, 1846), which took place shortly after the official outbreak of hostilities, seemed to indicate British acquiescence, for it granted the United States a free hand.

   Early in May, 1845, American troops under Gen. Zachary Taylor had been stationed at the Sabine River preliminary to an advance to the Rio Grande, the southern boundary claimed by Texas. They advanced to Corpus Christi in July. In Mar., 1846, after the failure of Slidell’s mission, Taylor occupied Point Isabel, a town at the mouth of the Rio Grande. To the Mexicans, who claimed the Nueces River as the boundary, this was an act of aggression, and after some negotiations Gen. Mariano Arista ordered his troops to cross the Rio Grande. On Apr. 25 a clash between the two armies occurred, and Taylor reported to Washington that hostilities had begun.



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