Feb. 25, 2023

The Mexican-American War

The Mexican-American War

In the 1840s, the United States was in a mad dash to expand its borders under the guise of manifest destiny, or the belief that it was God's will for the United States to extend its territory and spread democracy far and wide.

In 1846 this desire for increased territorial control led to military conflict with Mexico over the area including what would become California, Texas, New Mexico, Colorado, and New Mexico which ended with the Treaty of Guadalupe Hidalgo and Mexico ceding nearly half of its pre-war territory.

Tune in to hear about how manifest destiny, a rogue diplomat, and a future president contributed to the Mexican-American War.




DeLay, Brian. “The U.S. - Mexican War: Forgotten Foes.” Center for Latin American Studies. UC Berkeley. Fall, 2010. (LINK)


Katz, Jamie. “Why Abraham Lincoln was Revered in Mexico.” The Smithsonian Magazine. February 23, 2017. (LINK)


Pinheiro, John C. “James K. Polk: Foreign Affairs.” Miller Center. (LINK)

The American Yawp: A Massively Collaborative Open U.S. History Textbook, Vol. 1: To 1877. United States: Stanford University Press, 2019. (LINK)


Welcome to Civics and Coffee. My name is Alycia and I am a self-professed history nerd. Each week, I am going to chat about a topic on U.S history and give you both the highlights and occasionally break down some of the complexities in history; and share stories you may not remember learning in high school. All in the time it takes to enjoy a cup of coffee. 



Hey everyone, welcome back. 


A couple of weeks ago, I covered the political career and presidential administration of the eleventh president of the United States, James Polk. In that episode, I discussed one of Polk’s biggest accomplishments: acquiring more than a million square miles of land. 


Polk, committed to expansion as part of manifest destiny, worked diligently to secure extra territory. He negotiated with Great Britain for total control of the Oregon territory and went to war with Mexico over the landmass known today as California, Utah, Nevada, and New Mexico. This conflict permanently altered the borders of the United States and Mexico and reduced Mexico's territory by half. 


So, this week, I am diving into the Mexican-American War. How did it begin? And what legacy did it leave behind?


Grab your cup of coffee, peeps. Let’s do this. 


While the Mexican-American war did not officially begin until 1846, hostilities had been building for a decade. In the 1830s American slaveholders flooded into the Texas territory to take advantage of the fertile soil for cotton cultivation. As the Mexican government implemented a new constitution banning slavery, tensions quickly escalated, culminating in the Battle of the Alamo. I did a deeper dive into the fight and its outcomes back in 2021. If you want to learn more about the Alamo, look for episode 80 in the catalog or search for the episode title The Alamo on the website. 


In that episode, I mentioned that despite the success of the ragtag band of men in securing victory over General Santa Ana, the Mexican government refused to acknowledge Texas’ claimed independence, treating the territory as in rebellion. While several officials sought to add the self-titled Texas Republic to the union, sectional politics over slavery and maintaining the balance between slave and free states delayed any movement on welcoming the territory into the United States. 


However, by 1844, the country had manifest destiny fever, and support for Texas annexation proved to be pivotal in Polk’s bid for the presidency. Despite the loud opposition coming from the Whigs in Congress, the administration moved forward with adding Texas as the 28th state on December 29, 1845. As the Mexican government never recognized the Republic of Texas as a separate and sovereign territory, they were justifiably angry over the move calling it quote “an act of aggression, the most unjust which can be found recorded in the annals of modern history,” end quote. While vocal in their displeasure with the move, Mexico made no immediate acts of aggression against the United States. 


However, dispute over the two nations’ borders further deteriorated their already fragile relationship. The United States contended the Texas border sat along the Rio Grande as per the treaties of Velasco signed by General Santa Ana in the aftermath of the Battle of San Jacinto in 1836. Signed after the small army overwhelmed Santa Ana’s men in their vengeance over the Alamo, these agreements were, like Texas independence itself, not recognized by the Mexican government. However, even if they were to accept these agreements, they contended the Rio Grande was still incorrect as the river was known as the Rio Bravo. For Mexico, the proposed border was several miles to the north and sat along the Nueces River.


Missing from the conversation of course were the indigenous inhabitants of the land. Scores of Navajo, Apache, Comanche, and Kiowas had set up communities for themselves in the Nueces strip and had lived in the area under peace agreements since the 1700s. Tribes consistently and forcefully rebuked attempted incursions on their land, often violently repelling attempted Mexican settlements. These repeated raids diminished Mexican attempts to establish communities within the area, making the land appear to outsiders as empty. As historian Brian Delay explains, by the 1830s the indigenous tribes were considered by both the United States and Mexican governments to be troublesome, but that they were quote “no longer entities of national, let alone international, significance,” end quote. Instead, the native Americans were used as a scapegoat for the U.S. demand for                                                                                                                                                                                                                                                                                                                                                                                                                                    

territory, portraying the tribal nations as savages occupying land that only the United States could protect. In a message to Congress, President Polk perpetuated the sentiment by writing quote, “If New Mexico were held and governed by the United States, we could effectually prevent these tribes from committing such outrages, and compel them to release these captives, and restore them to their families and friends,” end quote. 


Despite their presence, the United States and Mexican governments preceded apace as if the land was empty and there for the taking. By July 1845, future president and military commander Zachary Taylor were stationed along the strip under the guise of protecting and securing the United States border. In November 1845, Polk sent John Slidell to Mexico City with an offer to purchase the debated Nueces strip territory, as well as portions of today’s California and New Mexico for twenty-five million dollars. Polk firmly believed Mexico would rebuff his offer, however, decided to appease those in Washington who were pushing for diplomacy over military conflict. The Mexican people, still angered at the theft of the Texas territory, were in no mood to hand over even more land to the United States, leaving the Mexican government in a precarious position. As Polk expected, the offer presented by the United States was heartily rejected. 


Anticipating the refusal, Polk ordered Taylor to march from his post along the Nueces strip towards Corpus Christi where he was then ordered to march into the disputed territory. Mexican authorities demanded Taylor’s retreat, which he steadfastly refused. Instead, Taylor built a makeshift fort. Polk and his administration had hoped the show of U.S. forces along the border would entice Mexico to return to the bargaining table, but the occupation only further angered the government and they made preparations for war. 


On April 25, 1846, Mexican forces attacked U.S. troops, killing 11 and capturing 52. This bloodshed was exactly the excuse Polk needed to convince holdouts of the need to escalate and declare war. In his request for a declaration, Polk asserted Mexico had quote, “repeatedly threatened to make war upon us for the purpose of reconquering Texas. In the meantime, we have tried every effort at reconciliation,” end quote. While an interesting take on the preceding events at best, at least a few members of Congress were still hesitant to sign on to the calls for war, including John Quincy Adams and John C Calhoun. Despite their opposition, Congress granted Polk’s request and declared war on May 13th, 1846.


At least one more future prominent politician took issue with Polk’s call for war, challenging the president to prove the loss of American life, insinuating the story told was not entirely accurate. That politician was the young freshman Whig from Illinois and future president, Abraham Lincoln. Not yet in office when the country voted for the war, Lincoln continued to question the constitutionality of the engagement, introducing eight spot resolutions questioning the war’s legitimacy. This proved unpopular in his home district and caused Lincoln to forgo seeking re-election. 


As described by historian John C Pinheiro, the war consisted of four phases. Taylor’s movement into the disputed territory was the first where he saw victories at both Palo Alto and Resaca de la Palma and captured the city of Monterrey. The second phase, overseen by General Stephen Watts Kerney, included troops marching toward Santa Fe, securing the city on August 18, 1846. Kearney’s men were then split and half went to join Taylor in Monterrey and the other half marched towards California to join Captain John C Fremont. While the United States continued its forward advancement, the Mexican government was in a bit of chaos. The country saw three separate presidents in 1846 alone, making coordinating a war effort especially difficult. During the third phase of the war, Polk and Alamo villain and Mexican exile General Santa Ana entered into secret negotiations. Santa Ana promised he would help end the war and secure peace between the two nations for a small payment of 30 million dollars. 


Of course, once back in Mexico, Santa Ana took the partial payments received from the United States and, instead of using the money to start peace talks, began to shore up Mexico’s defenses and was made Supreme Commander of the Mexican army. Back in military command, Santa Anna raised a new militia and marched towards Zachary Taylor’s troops still stationed in Monterrey. Jealous over Taylor's rising popularity and irritated with the military commander's implementation of strategic decisions without Polk's approval led the president to order half of Taylor’s men to vacate Monterrey and march toward General Scott who was preparing to lead an invasion of Central Mexico. 


Hobbled with a reduced fighting force, Taylor and his men met Santa Anna’s troops at the battle of Buena Vista on February 22, 1847, and, against all odds, overpowered Santa Anna’s men despite being outnumbered by a three-to-one margin. This victory proved politically important for Taylor, who earned the nickname Old Rough and Ready and he would later spin his military victories into a presidential win in 1848.   


The victory at Buena Vista was followed by the capture of Veracruz in March of 1847 and snowballed into a five-month campaign to overrun Mexico City, successfully securing the capital on September 14, 1847. Weakened by a string of overwhelming military defeats, the United States sent in diplomat Nicholas Trist to negotiate peace. This turned into a quagmire once Polk lost confidence in Trist’s ability to quickly secure peace and recalled the young diplomat, only for Trist to ignore the president’s orders and continue negotiations. 


Polk, wanting a quick end to the conflict with Mexico, became frustrated as peace talks continued to stall and wrote in his diary that Trist negotiated with quote, “no ability,” end quote. Believing he could secure Mexico’s compliance via other means, Polk issued three separate recalls to the diplomat through Secretary of State and future president James Buchanan. Upon receiving his third recall notice, Trist initially wrote to his wife and asked her to relay his receipt of the message and commitment to following orders. 


However, the Mexican government, perhaps unaware of the recall, urged him to continue negotiations. His ego inflated, Trist decided to stay and committed to securing a treaty with Mexico. In an odd rebuke, Trist wrote a 65-page missive addressed to Buchanan announcing his decision to ignore his recall notice and dedication to finalizing a peace treaty. Given the communication delays of the time, Polk was under the false impression Trist was on his way back to the United States, announcing such during his annual message on December 7, 1847. It wasn’t until January 5, 1848, that Polk learned of Trist’s insubordination when his wife Virginia showed up at the Secretary of State’s office with a coded letter informing her of his plans. 


Now on borrowed time, Trist worked quickly to secure and finalize a treaty, setting a deadline of February 1st with Mexico. His unconventional approach worked and the Mexican government agreed to a treaty on February 2nd, 1848. Named after the town in which it was signed, the Treaty of Guadalupe Hidalgo finalized peace between the two countries and outlined several parameters, including a payment of $15 million from the United States in exchange for Texas, California, and New Mexico and agreeing to the border along the Rio Grande. 


The Senate received and approved the treaty on March 10, 1848, with a vote of 38 to 14. Of those who voted no, half opposed the border along the Rio Grande, instead desiring the entirety of Mexico, and the other half completely opposed the war, to begin with, and therefore wanted none of the allotted territory. With the treaty, the United States increased its overall size holdings by 750,000 acres, or roughly 25%, and Mexico lost between a third and a half of its previously held territory. Over thirteen thousand Americans lost their lives in the conflict, though just 2,000 from combat as disease proved to be the biggest killer. The Mexican casualties totaled more than 50,000. 


The first military conflict widely covered by the press, the Mexican-American war helped promote the United States as a world power. It made yet another celebrity out of the military leader in Zachary Taylor, who, like Andrew Jackson after the battle of New Orleans in 1815, leveraged his newfound popularity to win the presidency in 1848. The war also forever altered the landscape of both the United States and Mexico and, many argue, served to further push the United States towards the Civil War. 


Before I sign off today, I wanted to do a quick reminder that I will be attending the Society for Military History Conference in San Diego next month. I am so excited to join Philip from Modern Scholars for a panel discussion about podcasting and history. If you are planning on attending, let me know. I would love to connect and geek out about history with you. 


Lastly, if you want to learn more about the source material, make a request, or learn how you can support the show, please visit the website at www dot civics and coffee dot com. 


Thanks, peeps. I’ll see you next week. 


Thanks for tuning and I hope you enjoyed this episode of Civics & Coffee. If you want to hear more small snippets from american history, be sure to subscribe wherever you get your podcasts. Thanks for listening and I look forward to our next cup of coffee together.