Mexican American War - 1846-1848 

Mexico started it - all by themselves!

Mexican General Arista

In a letter dated Apr 18, 1846, Paredes wrote to General Arista “It is indispensable that hostilities begin, yourself taking the initiative.”(92)

On April 25, 1846, 1,600 Mexican troops crossed the Rio Grande and ambushed a force of 80 American troops. Eleven men were killed and the rest taken prisoner. 

The US declares War on Mexico

President Polk received a report of the ambush on May 9.  On May 13, Congress declared war on Mexico. Although their was some opposition to the war, most Americans supported it - especially in the south. Approximately 75,000 men eagerly enlisted in volunteer regiments raised by the various states, including Massachusetts, where Whig opposition to the war was strongest. Thousands more enlisted in the regular U.S. Army. There was no need for a draft. In some places, so many men flocked to recruiting stations that large numbers had to be turned away. Thousands of newly-arrived Irish and German immigrants also heeded the call to arms.(100) In state after state, thousands more volunteered for the US Army then were needed.(101)

General Zachary Taylor

Before Congress could declare war, two more battles took place on the north side of the Rio Grande - at Palo Alto on May 8 and Resaca de la Palma on May 9.  The U.S. Army, comanded by General Zachary Taylor, won both battles, losing just 50 men.  Mexico lost over 1,000. Being certain of victory at Resaca de la Palma, General Arista's victory meal, being prepared at his camp nearby, was eaten that evening by American soldiers.

These two defeats of Centralists forces resulted in rebellion throughout much of Mexico against Parades.  On July 28, 1846, Parades turned the government over to his vice-president to take command of the Mexican Army.  On August 4, 1846, Paredes was overthrown and imprisoned. On Aug 22, the Federalists placed Valentin Gomez Farias in power and restored the constitution of 1824.  

Once again, Santa Anna got involved. Santa Anna, who was in exile in Cuba, informed President Polk that if he were allowed through the US blockade of Mexico and be restored to power, he would sell New Mexico and California to the US.  Santa Anna also wrote to the Mexican government that if he was able to return to the country, he  would lead the military battle against the US, but had no aspirations to return to political power. Santa Anna lied on both accounts. The US allowed Santa Anna back into Mexico on Aug 16, 1846, and he took charge of the war effort. Santa Anna also overthrew Mexican President Farias and declared himself president. 

Campaign in California

For over 200 years, Spain/Mexico gave California little attention and this huge area of land was sparsely settled. Most Mexicans in California - who referred to themselves as Californios, detested the despotic government in Mexico City.  Although the central government in Mexico City demanded the expulsion of Americans from California, the locals declined to follow the orders. In fact, about a third of the land that was given away went to Americans. As a result, American strength continued to grow.(102)

Commodore John Sloat
John Fremont

General Vallejo

In 1845, with tensions growing between the US and Mexico, John D. Sloat, commander of the US Navy ’s Pacific Squadron, was instructed to land in California and claim it for the US if war broke out. It was a tragedy that some US government and military officials didn’t recognize the profound political differences between Mexicans and Californios. While there was hatred between the US and Mexico, most Californios, led by General Marianno Vallejo, had strong pro-American feelings. These feelings were sorely tested after explorer John Fremont arrived in December, 1845. Despite orders to “conciliate the feelings of the Californians. . .” Fremont instigated numerous confrontations with authorities. Convinced authorities were about to forcibly expel him and his men and believing war between the US and Mexico was imminent, about 3 dozen men started what became known as the Bear Flag Revolt on June 10, 1845. Incredibly, the Bears took General Vallejo and other pro American Californios prisoner, took control of Sonoma and declared the Republic of California.

Sloat, not wanting to take action prematurely, waited until July 7, when Sloat’s men defeated a small detachment of Mexicans and raised the US flag at Monterey. A proclamation was then issued, declaring “the first importance to cultivate the good opinion of the inhabitants.”(103) By the end of July, some 160 settlers and US soldiers plus sailors and Marines from Sloat’s ships had seized all of northern California. Fremont met Sloat aboard the Navy ship Savannah and Sloat demanded to see his orders that authorized Fremont to take up arms against the Californians. Learning Fremont had no such orders, Sloat unleashed a blistering tirade against Fremont.(104) On July 29, Sloat ordered Vallejo released and the others prisoners were released soon afterwords. Most residents of northern California were elated and General Vallejo put his old Mexican military uniforms in a pile and set them on fire.(105)

The Mexicans, under Comandante Castro and Governor Pico, fled south to Los Angeles and prepared to defend the city with a force of 800 men. On August 10, a force of 360 sailors and Marines and 80 settlers approached the city but the Mexican force evaporated and US forces occupied the city the next day unopposed. On Aug 22, all of California was under US control and elections were scheduled for Sep 15 to choose municipal officials.

Unfortunately, things did not remain peaceful do to inept and heavy handed leadership by some US officials. On Sep 23, the uprising began and soon a force of over 300 Mexicans retook Los Angeles and by Oct 29, all of southern California was under control of local Mexicans. But the locals were halfhearted rebels, and most young men went into hiding when Mexican recruiters went looking for them. Within days, Americans retook San Diego and on Jan 2, 1847, went on the offensive. After several battles, Los Angeles surrendered on Jan 10 and this was the last fighting in the reconquest of California.

With both American commanders feuding over who was in charge, John Fremont, now a much wiser man, took the initiative and negotiated a generous peace treaty between the US and the Californios. The Treaty of Cahuenga was signed on January 13, 1847. All Mexicans involved in the rebellion were pardoned and asked to lay down their arms and return to their occupation. They were allowed the same rights and privileges as citizens of the United States, and would not be compelled to take an oath of allegiance until a treaty of peace was signed between the United States and Mexico. They could leave the country if they chose to, though nearly all stayed.

Conquest of New Mexico

General Stephen Kearny
Alexander Doniphan was an attorney, soldier and politician from Missouri. He refused a direct order to execute Joseph Smith, Jr., the founder of the Mormon faith in 1838. He lead an army of Missouri volunteers during the Mexican American War, decisively defeating the Mexican Army at El Paso and Sacramento River, about twenty-five miles north of Chihauhau, Mexico. Doniphan and his men marched nearly 5,500 miles during the conflict, the longest march since Alexander the Great.

On July 31, 1846, Colonel Kearny issued a proclamation to “the citizens of New Mexico,” advising that he was entering that territory “. . . with a large military force for the purpose of seeking union with and ameliorating the conditions of its inhabitants. . . They will not be interfered with by the American Army, but will be respected & protected in their rights both civil & religious.”(106) On Aug 1, Kearny sent a letter to Governor Armijo, advising that he came “as a friend and with the disposition and intention to consider all Mexicans and others as friends . . . Such persons shall not be disturbed by any one under my command either in their Persons, their Property or their Religion.”(107)

On Aug 15, despite warnings that Armijo was planning a major battle for Las Vegas, no army was present. Most Mexicans living under Armijo despised the man and few were willing to fight for him. Later, Armijo fled south for fear of being assassinated by his own people. There was a public ceremony where New Mexico was proclaimed now part of the U.S. and citizens were promised protection of their property and especially protection from the dreaded Navajos and Apaches. This ceremony was repeated in other villages. The people recognized they had nothing to lose and everything to gain by becoming part of the U.S.

On Aug 18, Kearny’s forces rode unopposed into the village of Sante Fe. The Lieutenant Governor Juan Aland served wine and brandy to Kearny and the next day, Kearny gave the oath of allegiance to the United States to the towns people.(108)

The northern part of the territory was under U.S. control. On Sep 22, a new government was established with Charles Bent the first Governor.


Kearny and 300 men then left to join in the California campaign being replaced by volunteers from Missouri led by Alexander Doniphan. Days later, Kearny’s men discovered the Mexican town of Pulvidera had just been raided by Apaches. All the men had been killed and the horses and women taken. The women would be treated as slaves for the rest of their lives. Kearny ordered Doniphan to subdue the Indians before going south to fight against Mexico. After 7 weeks, The Indians agreed to a peace treaty and Doniphan left Santa Fe for the war with Mexico.(109) On Christmas of 1846, just 30 miles from El Paso, a battle between Mexican forces and Missouri volunteers left over 100 Mexicans dead. The Americans then occupied El Paso.

Meanwhile, the bullying attitude of some American volunteers in Santa Fe caused the locals to feel abused rather than protected. On Jan 19, 1847, Governor Bent, visiting in Taos, was killed and about 20 more Americans were killed over the next several days.  On Feb 2, a US force of close to 500 troops surrounded an area north of Taos where the rebels were making their stand. About 150 rebels were killed and the rest surrendered. Following this ordeal, the area remained peaceful.

Mexico must be conquered!

Amphibious Landing in Mexico

General Winfield Scott

Initial U.S. strategy was to defend Texas and then attack across the Rio Grande into Mexico and conquer the Mexican territories of New Mexico and California. This, it was hoped, would persuade Mexico to negotiate a permanent peace with the U.S. By August, 1846, these lands had been conquered. But with Mexico still refusing to negotiate, a heated debate took place in Washington on how to prevent this war from dragging on indefinitely. General Taylor’s opinion was that we had already conquered enough territory to pay all of our monetary claims against Mexico, and we should just stop the war and force Mexico to undertake any future offensive operations. Many in the U.S. favored this idea over a long war of attrition.(110)  

Landing at Vera Cruz
General Scott and the US Army march into Mexico City

Ultimately, this idea was rejected. Such a defensive plan was precisely what the Mexicans, whose ancestors had fought the Moors of Spain for hundreds of years, desired. It was exactly this policy of endless war against Texas that had propelled Texas to join the American Union for her own defense. Endless war with Mexico would have required a large and continuous military force on the border and eroded national resolve.(110)  By November, Polk realized that Mexico had to be conquered.  U.S. forces would have to occupy or threaten Mexico City and that it would be best to approach it from the Gulf coast, rather than from the north, taking the same route Cortez followed three centuries earlier when the Spanish conquered the Aztecs.(110)

On March 1847, General Winfield Scott made his amphibious landing near Vera Cruz with about 12,000 men. Over the next 5 months, the American Army, with less then 15,000 men repeatedly outmaneuvered, outsmarted and decisively defeated Santa Anna and the Mexican Army.

In June it was learned from an English delegation that Santa Anna was willing to talk peace to end the war. The U.S. was to send him $10,000 in cash so that he could influence the necessary people. The money was given to Santa Anna, but it turned out to be another scam.(111)

Unable to maintain a secure supply line, Scott lived off the land. Mexicans eagerly sold Scott all the food and supplies he needed because the U.S. Army paid in cash. On September 13, 1847, Scott’s men entered Mexico City. Santa Anna, the “Napoleon of the West” turned the government over to Pena y Pena, the president of the Supreme Court of Justice, and fled the country.

Scott’s 5 month conquest of Mexico was one of the most brilliant military campaigns in history. After predicting a disaster for Scott, the Duke of Wellington wrote, ”His campaign was unsurpassed in military annals.” The amphibious landing at Vera Cruz was the largest in history to that time.

Continue to "Peace Treaty of Guadalupe Hidalgo and Aftermath of the War."

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