Causes of the Mexican American War of 1846

Mexico refuses to recognize Texas independence or negotiate

In January, 1838, President Bustamante addressed the Mexican Congress and said: “With regard to the Texas campaign, I will only observe that its prosecution is the first duty of the Government and of all Mexicans.”(32a)

When Santa Anna opened Congress in 1842, he said regarding the Texas question: “If we wish to preserve an honorable name among civilized nations, it is essential that we employ all our energies and resources in combating without cessation, at any sacrifice and at all hazards, until our arms and our pretensions finally triumph.”(32b)

With Mexico refusing to honor the peace treaty, and threatening perpetual war with Texas, Texans in September 1837 voted for annexation by the US.(32c) Because of the slavery issue and fear of getting involved in a war with Mexico, Texas was not allowed to join the union.

By 1839, Texas was in negotiations with Mexico in the hopes that they would recognize Texas independence. Ironically, in the Autumn of 1839, General Antonio Canales visited Texan officials seeking help in rebelling against the Mexican government. The Mexican states of Coahuila, Nuevo León, and Tamaulipas wanted to form their own country called The Republic of the Rio Grande, with Laredo as the capital. The Texas government passed resolutions forbidding Texans to help Canales. Texas hoped that by staying out of this latest rebellion against the central government, Mexico would reward Texas with recognition of their independence.(33) But 160 Texans, seeing the chance for a peaceful neighbor to the south, fought with Canales anyway.(34)

The Republic of the Rio Grande ended In November 1840, when Gen. Canales and Mexican General Arista met to discuss the war. Mexico offered General Canales the position of brigadier general in the Mexican army in exchange for his abandoning the cause of the rebellion. Canales accepted and the rebellion ended.(35) Texas continued to negotiate with Mexico up to 1841, but got nowhere.(33)

When Santa Anna regained power in October 1841, Mexican hostility against Texas resumed: 
• On March 5, 1842, a Mexican force of 500 men invaded Texas and briefly occupied San Antonio, but then fled back to Mexico.(36)(37)

• On September 11, 1842, San Antonio was again captured by a force of 1400 Mexican troops.(36)(37) A Texan force sent to recapture San Antonio became involved in several bloody battles, including an engagement in what became known as Dawson’s Massacre.(37)(38) The Mexicans then retreated back across the Rio Grande but took a large number of prisoners to Perote Prison near Vera Cruz. It was believed that Mexico would next attack Austin, hoping that a capture of the capital would be the end of Texas independence.(37)

• Mexico ordered two war steamers from England. Texas had reason to believe these would be used to occupy Galveston - which would destroy the Texas economy. In March 1842, every citizen of Galveston not in the army was called upon to labor in constructing defensive batteries.(39)

By 1843, Texas was in bad shape. The economy was bad, no standing army to defend against Mexico and the Treasury was empty. Santa Anna saw an opportunity to reconquer Texas, but fortunately for Texas, another rebellion in Mexico, this by Yucatan, occupied Santa Anna. In February 1843, Santa Anna sent a proposal to Sam Houston: If Texas would accept Mexico’s sovereignty and be re-incorporated, Texas could retain control of her own internal affairs and Mexico wouldn’t put troops in the state. A short time later, Mexico’s Secretary of Foreign Relations informed the British that soon Mexico would attack Texas in the most ruthless manner. The Brits passed the message to the Texans.  Two months later, believing Texans would be more inclined to accept his proposal with some threats, Santa Anna reminded Texans of the massacres Mexico had committed at Goliad and the Alamo!(40A) 

In May, 1842, Mexico protested against the aid given to Texans by citizens of the U.S. with the toleration of the U.S. government - 6 years after Texas became an independent country.(40B) By now, Texans recognized that Mexico would never recognize their independence and would conduct harassing raids, threaten and possibly invade Texas again. Texans would NEVER trust or rejoin Mexico. Texas longed for a final solution.

It is ironic that Mexico expected Spain to recognize THEIR independence, but when the tables were turned, Mexico refused to even consider this course of action for Texas.  Spain recognized Mexico as an independent country in 1836 - 15 years after their successful revolution.  Mexico should have recognized Texas as an independent country as they no longer had any justifiable claim to the territory - Santa Anna DID sign a peace treaty with Texas.  The Texas Republic was recognized as a free, sovereign nation by the US (1837), followed by France, Great Britain, Holland and Belgium.

Jose Bocanegra

All attempts at diplomacy over the issue of Texas were rejected by Mexico. In August 1843, Mexico’s secretary of relations, Bocanegra declared “...the Mexican Government will consider equivalent to a declaration of war against the Mexican Republic the passage of an act for the incorporation of Texas with the territory of the United States; the certainty of the fact being sufficient for the immediate proclamation of war...”(52)(53) These threats of war were issued several more times. In 1844, Santa Anna was given 4 million for war with Texas.(54) 

In addition to the impasse over Texas, Mexico refused to pay compensation to US citizens - stalling for years.(99A)(99B)(99C) On 5 Apr 1832, the U.S. and Mexico signed a treaty of amity, commerce and navigation. It was after this that grievances began to pile up. There were off and on negotiations with Mexico plus additional grievances were filed. Unable to come to a resolution, the U.S. and Mexico agreed to have an international umpire decide what grievances were legitimate and for how much. Baron Roenne of Prussia was the ‘umpire.’ The commission started on 17 Aug 1840 and ended on 26 May 1841. Baron Roenne made decisions on claims worth $6,648,812 and Mexico was held liable for $2,026,139. Eight claims were rejected on merit and ten on jurisdiction. Thirty six claims were valid - either wholly or partially.(99D) Mexico was to make 20 quarterly payments for 5 years but after 3 payments, Mexico failed to make their April 1844 payment.

In September 1844, Mexicans revolted against Santa Anna’s ever increasing corruption and dictatorial ways. He tried to flee the country, but was captured in January, 1845 and exiled to Cuba.(29) Jose Herrera was installed as acting president of Mexico. On July 21, 1845, shortly after Texas accepted the US annexation offer, Herrera announced a resolution promising to declare war on the US whenever American troops “invaded” Texas.(54B) In the summer of 1845, Mexico gave official notice to England and France that war was inevitable.(55) The popular “La Voz del Pueblo” ranted “Extermination and death to the Sabine [River] was the cry of our victorious legions at the Alamo, Bejar and El Salado. Extermination and death will be the cry of the valiant regulars and of the citizen soldiery, marching enthusiastically to conquer Texas.”(56A)

Mexico now blamed Texas for its escalating war with Indian tribes, especially the Apaches and Comanches. Early in 1845, Texas had signed peace agreements with the Indians, who turned their fury against Mexico. The truth is that the Indians had waged wars against Mexico for several centuries, but this was just another way to spew hate against Texas and ultimately the U.S.(56B) 

President Herrera
John Slidell

The US continued its efforts for a negotiated settlement. In October, word was received that Herrera was prepared to discuss all differences with the U.S. John Slidell, a man who spoke fluent Spanish was sent to Mexico and arrived in Mexico City on 6 December.  He had “full powers to adjust and definitively settle all pending differences between the two countries, including the boundary between Mexico and Texas.”(57) 

Slidell was also to attempt to buy New Mexico and California. The US believed Mexico would be willing to sell these lands as Mexico was constantly on the verge of bankruptcy with a staggering national debt, had scarcely any citizens on the land and had very little control over the area. Indians attacked Mexican settlements at will, as Mexican authorities did not have enough military personnel on hand to stop them.  Unfortunately, by December, 1845, the Herrera government was about to be overthrown, and in a futile attempt to save itself, refused to meet with Slidell.(58) 

Trying to justify their refusal to meet with Slidell, Mexico claimed they could only meet with a commissioner. Slidell, who had been credentialed as a minister, was then made a commissioner. Mexico still wouldn’t meet with Slidell, showing that Mexico was quibbling over the mere form of Slidell’s credentials for the purpose of evading negotiations. Paredes also refused to meet Slidell.

Americans were demonized by nearly every politician in Mexico. Trying to outdo the other with never ending hate speech against the U.S., John Slidell wrote in September 1845: “The most stubborn and malignant feeling seem to exist in the mind of every Mexican against the United States.“(59) Later, Slidell summed up his experiences with Mexico: “We shall never be able to treat with her on fair terms until she has been taught to respect us. . . here all amicable advances are considered as indicative either of weakness or treachery.” Slidell added privately to James Buchanan, “Be assured, that nothing is to be done with these people, until they shall have been chastised.”(60)

Critics of the U.S. claim that attempting to buy this land was “insulting” to Mexico. But the US purchased land from Spain, France. There is nothing offensive about asking to buy land. You can just say ‘no.’ This accusation is unwarranted. 

In 1842, US Navy Captain Thomas Jones, created a political storm in the U.S. and Mexico. After hearing false news that war had broken out between the U.S. and Mexico and the British were preparing to seize California, Jones captured Monterey, California on Oct. 19, 1842. The next day Californios informed Jones that there was no such war. Jones hauled down the U.S. flag, ran the Mexican flag back up, paid the Mexicans for damages and sailed away. After an investigation, Jones was relieved of command of the U.S. Navy Pacific Squadron.(61)

It should be noted that the issue of the Oregon Territory with Britain was settled peacefully after long and extremely difficult negotiations.(62) Mexico refused to negotiate at all.

The U.S. decides to bring Texas into the Union

With negotiations a failure, Texas began to explore other options.  One was to align itself with Britain for protection from Mexico. Another option was discussed in May 1843, in Ashley, South Carolina when a group of southern states met to discuss seceding from the US, joining with Texas and forming a new country.(41)(42)  A third option was to join with California and Oregon and form a new nation.  The desire of Californians to be free of Mexican rule was growing stronger all the time.(43)

By 1845, time had run out for the U.S. to make a decision on Texas. The U.S. feared commercial and political agreements between Texas and European countries that would make annexation imposible in the future. It was widely believed the British were working to take control of California from Mexico and attempting to align themselves with Texas. The war of 1812 against the British was still a traumatic event for many people and fear of British expansion into the western part of the continent was a legitimate concern. If the US did not annex Texas now, Texas would never become part of the US. 

In April 1844, the US agreed to annex Texas into the union.  In May, 1844, a US military buildup of several thousand men was begun at Fort Jessup in Louisiana, to observe the Texas border. About the same time, a US representative met with Santa Anna’s representative and explained that the US was compelled for its own security to negotiate a treaty for annexation with Texas.  The border and monetary compensation was put on the negotiating table.  Mexico’s response was belligerent and non-compromising.(44) However, the annexation treaty lost in the Senate in June, 16-35.(45) The reasons were the slavery issue and not wanting to offend Mexico. 

President Tyler
Juan Almonte

But when James Polk won the Presidency in November, 1844 on a platform of annexing Texas and Oregon, President John Tyler submitted a new treaty to Congress in the form of a joint resolution to bring Texas into the American Union. There was still opposition to admitting Texas because it would add another slave state and strengthen the south. However, the greater fears were British expansion and Mexico’s continuous belligerence towards the U.S. which changed public opinion.

On February 28, 1845, six days before Polk took office, Congress passed the joint resolution for annexing Texas.(46A) In the Senate, fourteen slave state and thirteen free state men voted for the resolution, and twelve slave and thirteen free state men against it. In the House, sixty-seven slave state and fifty-three free state men were infavor of it, and eighteen slave and eighty free state men against it.(46B) Mexico broke off diplomatic relations with the U.S. Mexico’s minister in Washington, Juan Almonte, declared his country would maintain the claim to her former province “at all times, by every means . . . in her power.”(47) On Apr 9, 1845, Almonte described the annexation of Texas as “an act of aggression the most unjust which can be found recorded in the annals of modern history.”(48)

Polk defends admitting Texas to the United States

President Polk

Newly elected President James Polk defended admitting Texas into the Union in his March 4, 1845 Inaugural speech: “I regard the question of annexation as belonging exclusively to the United States and Texas. They are independent powers competent to contract, and foreign nations have no right to interfere with them or to take exceptions to their reunion. Foreign powers do not seem to appreciate the true character of our Government. Our Union is a confederation of independent States, whose policy is peace with each other and all the world. To enlarge its limits is to extend the dominions of peace over additional territories and increasing millions.”(50)

“None can fail to see the danger to our safety and future peace if Texas remains an independent state or becomes an ally or dependency of some foreign nation more powerful than herself....Whatever is good or evil in the local institutions of Texas will remain her own whether annexed to the United States or not. None of the present States will be responsible for them any more than they are for the local institutions of each other.... Upon the same principle that they would refuse to form a perpetual union with Texas because of her local institutions our forefathers would have been prevented from forming our present Union.”(50)

Faced with imminent American annexation of Texas, the British Minister to Mexico, Charles Bankhead and the French minister to Mexico persuaded Texas to sign their Peace Treaty on 29 March 1845, in which Mexico would recognize the independence of Texas, with boundaries that would be determined with French and British mediation. But Mexico made changes and didn’t sign the document until 19 May, 1845, enraging Bankhead. The offer was finally presented to Texas, but it was too late. No one trusted Mexico.(49A) (49B) On July 4, 1845, Texas Congress accepted the US annexation offer and rejected Mexico’s offer. On Oct 13, 1845, Texans voted to accept annexation into the US by 7,664 to 430.(46A)  Also in October, about 3900 US troops gathered at Corpus Christi to ensure safety for Texas.(51) On December 29, 1845, Texas officially became the 28th state in the United States.

Herrera overthrown, Paredes takes power

General Paredes

Opponents of Herrera used the issue of Texas independence to further incite Mexican hatred of America, whip up war fever and undermine Herrera. In  August 1845, the Centralist’s leader, Mariano Paredes, demanded an attack on the United States. On Jan 2, 1846, Paredes marched into Mexico City at the head of the army.(63) Herrera fled for his life. On Jan 4th, Paredes took the oath of office as the new president and claimed all of Texas to the Sabine River - which separates Texas from Louisiana.(64)  

This is the same Paredes who attempted to start a war with the U.S. in 1841. On August 8, 1841 he joined in a revolt against the regime of Anastasio Bustamante, whom he accused of not fighting to recover Texas. Francisco Echeverría was chosen interim president, but within a short time, Santa Anna assumed the presidency. Paredes was pushed out of power and he became an enemy of Santa Anna. Later, in November 1844, after the U.S. agreed to annex Texas, Paredes declared war had begun against the U.S. On March 12, foreign Minister Jaoquin Maria del Castillo y Lanzas forwarded a message to Slidell which stated that Paredes would not meet with him but hoped to resolve the situation peacefully. On Mar 21, Paredes vowed that Mexico “does not recognize the American flag on the soil of Texas. . .”(65)

Mexico certain of victory

Paredes confidently believed his experienced army would crush the Americans and their small army.  The Mexican Army had about 32,000 men, far more than the US Army.(66) Paredes army was well disciplined and very experienced in battle from many revolutionary wars in Mexico.  Parades also believed that the U.S. would have a hard time keeping their army supplied so far from population centers and prevent the US from using a large force against Mexico.(67)(68) 

Many Mexicans believed their army was nearly invincible. The Spanish Minister in Washington, Calderon de la Barca, said “There are no better troops in the world, nor better drilled and armed, than the Mexicans.”(69) The Mexican correspondent to the London Times stated in 1845 that Mexican soldiers “are superior to those of the United States.”(69) The Boletin Official of San Luis Potosi stated: “We have numerous and veteran forces burning with a desire to gain immortal renown.”(69) “Not to speak of our approved infantry, our artillery is excellent, and our cavalry so superior in men and horses that it would be an injustice not to recognize the fact.”(69) An editorial in La Voz del Pueblo said, “We have more than enough strength to make war.”  “Let us make it, then, and victory will perch upon our banners.”(68) Juan Almonte, a military man, assured his government that it was “certain” that Mexico would defeat the U.S.(123)

Many international observers believed the U.S. would have a tough time defeating Mexico - and many thought the US would lose. The British minister in Texas, Captain Elliot, stated “They [US troops] could not resist artillery and cavalry in a Country suited to those arms.”(70) The British weekly Britannia said the US is “fit for nothing but to fight Indians.”(70) Mexicans looked at the poor performance of the U.S. military in the War of 1812 with satisfaction.(70) Some foreign observers believed it would take 250,000 US troops to win. Other observers stated that it would be nearly impossible to defeat Mexico - a nation of over 7 million people with many rugged mountains. The ability of Mexico to wage guerrilla war against our supply lines would prevent us from massing sufficient troops to defeat the Mexicans deep in their territory. Mexico could outlast the U.S. without suffering disastrously, while the US would have to wage an extremely costly war, raise a large army and still not be able to defeat Mexico. Eventually the Americans would tire of the war, the never ending casualties, huge military spending and make peace on Mexico’s terms.(71)

The US never believed victory over Mexico was a sure thing, which was why it took so long to allow Texas to join the union and why we bent over backwards to peaceably resolve all the issues. 

Mexico also hoped that Europe - mostly Britain - would help them win their war against the United States. Britain, which recognized the independence of Texas and had fought two wars with the U.S., refused to get involved. On June 1, 1846, British Foreign Secretary Lord Aberdeen sent this message to England’s Ambassador to Mexico, Charles Bankhead: “She [Great Britain] would find herself engaged in a war with a Nation with which she would have no personal cause of quarrel, in behalf of a Nation and Government which she has repeatedly warned in the most friendly and urgent manner of their danger, and which, solely in consequence of their willful contempt of that warning, have at last plunged headlong down the precipice from which the British Government spared no efforts to save them.” Bankhead was instructed to make these points when informing Parades why Britain would not become involved in the war.(72)(73)

On Jan 12, 1846, Polk received word from Slidell that negotiations had failed. Polk realized that war with Mexico was inevitable. On Jan. 13, 1846, He ordered General Zachary Taylor to move his army from Corpus Christi to the north side of the Rio Grande River and prepare to defend Texas from a possible Mexican invasion.  Taylor received these orders on Feb. 3. The order to Taylor stated that “It is not designed, in our present relations with Mexico, that you should treat her as an enemy,” but “should she assume that character by a declaration of war, or any open act of hostility toward us, you will not act merely on the defensive, if your relative means allow you to do otherwise.”(74)

Before leaving Corpus Christi, General Taylor wrote a proclamation to the people of Matamoros in which he alerted them to his march, promised that his intentions were peaceful and vowed to respect their religious freedom and civil rights of the people he encountered. He also vowed to pay market value for any goods purchased.(75) Taylor’s army left Corpus Christi for the Rio Grande River on March 8. Despite the war rhetoric coming from Paredes, Polk still hoped to settle the disputes peaceably. Mexico made herself believe that General Taylor was going to invade Mexico. This was just more self induced hysteria on Mexico’s part and a way to arouse patriotic fervor in Mexico.

On March 19, at a stream called Arroyo Colorado, Mexican scouts presented Gen. Taylor with a proclamation by General Francisco Mejia, denouncing the U.S. advance and promising that the Mexican army would turn back the Americans and launch a counterstrike for the reconquest of Texas.(76) Mejia then issued a proclamation to Mexicans living near the Rio Grande River: “For what Mexican worthy of the name can resign himself not to fight to the death and so to see his noble race under the detestable domination of the foreigner?”(77)

Taylor’s force of about 4,000 men arrived on the Rio Grande on March 28, 1846. General Taylor again wrote letters to both civilian and military authorities across the river at Matamoros, expressing his desire to “enter into any arrangements to secure the peace and harmony of the frontier” until the US and Mexican governments could reach an official accord.(78) This force was HALF of the entire US army.(79) Surprisingly, Mexico only had a force of about 2000 men(80) including 20 artillery pieces(81) across the river at Matamoros though thousands of reinforcements were expected to arrive soon. 

These reinforcements took much longer to arrive then expected. Locals refused to sell supplies to their own army because they were “paid” in promisory notes - which were worthless. Mexican officials were enraged when Mexicans eagerly sold food, cloth and horses to the American Army which paid in cash.(82)

Face off on the Rio Grande River

On Mar 19, Mejia received orders to retreat from arroyo Colorado to defend Matamoros, He then built a large round fort of earth, timbers and brick to guard Anacuitas, the primary crossing into the city. Dubbed Fort Paredes, it could shelter up to 800 troops and occupied one of the highest points along the Mexican side of the Rio Grande.(83)

On March 29, the morning after the US Army arrived on the Rio Grande, Mexico put in place one 8 pound cannon aimed at the American camp and began to build elaborate defenses for Matamoros. By April 7, many more cannons were aimed at the US camp from multiple locations on the Mexican side.(84)

On Mar 29, American troops responded with 3 cannons, one of them pointing at General Mejia’s headquarters. By Apr 7, the US had built a redoubt and mounted four 18 pound cannons aimed at the public square in Matamoros.(85) On April 7, the US began construction of their own fort, which became known at Fort Brown.(85)

Gen. Pedro Ampudia arrived on Apr 11 with about 3,000 additional troops. He replaced Mejia. Ampudia had a reputation for needless cruelty. He had executed a man named Francisco Sentmanat in 1844 and fried his head in oil for display in the public square of San Juan Batista.(86) The locals had a strong dislike for Ampudia and petitioned Paredes for a change in leadership. On Apr 15, Ampudia was replaced by General Arista. Ampudia was now second in command.(87)

On Apr 11, Ampudia ordered all American citizens evicted from Matamoros immediately and sent to the interior of Mexico. There were about 300 hundred foreign nationals in Matamoras, the majority American.(88) The Americans were forced, sometimes at bayonet point, to walk 150 miles south to the city of Victoria.(89)

On Apr 11, Ampudia sent a communication to Taylor: “I require you” to retire to the north side of the Nueces River within “twenty-four hours,” while the U.S. and Mexican governments negotiate. Taylor rejected Ampudia’s ‘order’ and replied that an envoy - John Slidell - had previously been sent by the U.S. to Mexico for that purpose to no avail and he would remain on the north side of the Rio Grande River pending orders from Washington.(5)

On April 25, 1846, about 1,600 Mexican troops crossed the Rio Grande and ambushed American troops. The war was on.


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