The Mexican-American War

Podcast Transcript

After several years of rising tensions, on May 13, 1846, the United States Congress declared war on the nation of Mexico.

The war lasted only two years, and the conduct of the war was decidedly one-sided.

The conclusion of the war resulted in changes to both countries, which can be seen on the map and felt on the ground today. Yet, despite being one of the most important conflicts in the history of both countries, it has been largely forgotten today.

Learn more about the Mexican-American War, its causes, and its resolution on this episode of Everything Everywhere Daily.

The Mexican-American War is one that has largely been forgotten. Most people might know that there was such a war, but they would be hard-pressed to tell you the reasons for the war or anything specific about it.

If you roll back the tape of history, it seems almost inevitable that the United States and Mexico would eventually have some sort of conflict.

The United States became independent from Britain in 1776. Mexico became independent from Spain in 1821.

After independence, the United States began moving westward. The Louisiana Purchase in 1803 almost doubled the size of the country. More people began moving further west in search of land.

Many Americans believed that they had a manifest destiny to eventually control everything from the Atlantic to the Pacific.

The land that was part of Mexico in the early 19th century was land that had been claimed by Spain centuries earlier. The core of Mexico and the vast majority of the population and economy were located in the south. Far from the regions that today we call Texas, California, and the American Southwest.

This region had a very light presence by Mexico, given its distance from the capital, Mexico City.

As migrants began moving into this region, they mostly came from the East and were English-speaking, not Spanish-speaking. Due to geography, they found it much easier to trade with the Americans to the east than with the Mexicans to the south.

The settlers in Texas, here I’ll refer you to my episode on the history of Texas, declared independence from Mexico in 1836. Something which was not recognized by Mexico, who treated Texas as a rebellious province.

The event that started the United States and Mexico down the path of war was the vote by Congress to annex Texas and admit it into the union on March 1, 1845.

In response to the vote, Mexicans removed their diplomats from the US.

One of the major issues was that Texas said their southern border was the Rio Grande River, and Mexico said it was the Nueces River, further north.

On March 4, President James Polk took office, who was a big advocate of Texas joining the union and of the US spreading westward.

In November 1845, Polk sent an envoy, John Slidell, to Mexico to meet with the Mexican government. His mission was to make an offer to purchase California, which was another outstanding issue between the two countries.

He was told to offer a maximum of $25 million dollars to purchase California. However, the Mexican refused to meet with him.

In early 1846, U.S. troops under General Zachary Taylor moved into the disputed region between the Nueces River and the Rio Grande.

In order to solidify its claim to the area, President Polk sent a small force of 80 men to south Texas, just north of what is today Brownsville, led by Captain Seth Thornton.

On April 25, 1846, a Mexican force attacked the patrol led by Captain Thornton, killing or capturing all the soldiers. Polk used this skirmish—known as the Thornton Affair—as justification for war.

In many ways, this is exactly what President Polk was waiting for. They could now claim that they were attacked and that Mexico started the war.

Zachary Taylor’s forces defeated the Mexican army near the Rio Grande at the Battle of Palo Alto on May 8 and at the Battle of Resaca de la Palma on May 9.

On May 13, 1846, Congress declared war on Mexico, with Polk claiming that “American blood has been shed on American soil.”

Support for the war was not universal. There was a significant faction of Americans who were against going to war, especially in the North. The likes of Abraham Lincoln and Henry David Thoreau opposed the war as an unjust expansionist conflict.

They figured if the United States was born of revolution, they shouldn’t be doing the exact same thing European powers were doing.

The Bear Flag Revolt was an uprising by American settlers in California against Mexican rule in June 1846, during the early stages of the War.

Inspired by the expansionist beliefs of Manifest Destiny and tensions over Mexico’s control of the region, a group of settlers led by William Ide and John Frémont seized the town of Sonoma on June 14, 1846. They declared California an independent republic and raised a makeshift flag featuring a bear and a star—hence the name Bear Flag Revolt.

However, the rebellion was short-lived, as U.S. naval forces took control of Monterey and San Francisco in July 1846, officially placing California under U.S. military rule. The Bear Flag Republic lasted only a few weeks before California was absorbed into U.S. territory.

In August 1846, General Stephen Kearny led the Army of the West into Santa Fe, New Mexico, facing no resistance as Mexican Governor Manuel Armijo fled without a fight. Kearny peacefully took control of the city, declared New Mexico a U.S. territory, and established a military government, ensuring a swift and bloodless annexation.

By this time, just a few months into the war, the United States had taken most of what it wanted.

It demanded a surrender from Mexico so they could negotiate terms, but Mexico refused.

So, the decision was made to push further into Mexico.

U.S. forces under General Zachary Taylor advanced into northern Mexico.

The Battle of Monterrey took place from September 20 to 24, 1846. The city of Monterrey, a heavily fortified position defended by General Pedro de Ampudia, was strategically important for controlling northern Mexico.

The U.S. launched a three-day assault, facing fierce resistance from Mexican troops entrenched in strong defensive positions, including forts and barricaded streets. After intense urban combat, Taylor’s forces, aided by artillery and flanking maneuvers, gained control of key positions, forcing Ampudia to negotiate a capitulation. Taylor agreed to an eight-week armistice, allowing the Mexican army to withdraw, a decision criticized by President Polk, who wanted an immediate push further into Mexico.

The war, up to this point, was a string of American victories. There was a reason for that.

The United States had a huge advantage in almost every metric. Its population was three times the size of Mexico’s, and its economy was even larger. Despite the advantage in resources, Americans were actually outnumbered in almost every battle.

Moreover, they had more modern weapons compared to the Mexican army, which used decades-old firearms.

The Mexican Army was also nowhere near the level of the US Army in terms of professionalism. Ulysses S Grant, who served as an assistant quartermaster, later wrote the following in his biography:

“The Mexican army of that day was hardly an organization. The private soldier was picked from the lower class of the inhabitants when wanted; his consent was not asked; he was poorly clothed, worse fed, and seldom paid. He was turned adrift when no longer wanted. The officers of the lower grades were but little superior to the men”.

The Mexicans also had another huge problem: political turmoil. During the two-year span of the war, they switched presidents nine times. Many of them were more concerned with consolidating their power than they were with fighting the United States.

The Battle of Buena Vista occurred on February 22–23, 1847, in northern Mexico, where General Zachary Taylor and his 5,000 U.S. troops faced off against General Antonio López de Santa Anna and his 15,000 Mexican soldiers.

Taylor’s forces used superior artillery, defensive positioning in a narrow mountain pass, and tactical maneuvering to repel multiple Mexican assaults. Santa Anna, believing he had weakened the U.S. line, demanded Taylor’s surrender, but Taylor famously responded, “Tell him to go to hell!”

After intense fighting, the Mexican army suffered heavy losses and, short on supplies, retreated, allowing Taylor to claim victory.

The battle cemented Taylor’s reputation as a national hero and helped propel him to the U.S. presidency while also marking the last major Mexican offensive of the war.

About two weeks later, on March 9, 1847, General Winfield Scott led an amphibious landing at Veracruz. He took the city immediately and began to march towards Mexico City, following the same route that Hernán Cortés took over 300 years earlier.

Scott gradually made his way toward Mexico City, fighting with the Mexicans who fought defensive battles to slow him down. He won battles at Cerro Gordo in April, Contreras and Churubusco in August, and Chapultepec in September.

On September 14, 1847, U.S. troops entered Mexico City, effectively ending the war.

Because the Mexicans didn’t pursue terms earlier, once the Americans were in Mexico City, they had little leverage. Their only option was now a guerilla war, which they had a difficult time doing, considering the internal divisions within Mexico.

The Americans had never intended to go so far into Mexico. There was talk of annexing all of Mexico now that they were occupying most of it.

Oddly enough, while it was mostly Northerns who initially objected to the war, it was Southerners who objected to the annexation of Mexico. They were concerned that Mexico, which had mostly an Indigenous population, would skew the racial balance of the United States.

Both sides had an incentive to come to the negotiating table. The Americans didn’t want to be occupying Mexico any longer. It tied up their troops, and too many Americans objected to the United States being an occupying force.

The Mexicans realized it was the only way to get rid of the Americans. They also accepted the reality on the ground. Their territories to the north were lost. Texas had been gone for over a decade at this point. California had a rebellion and was occupied.

Much of the rest of the territory was desert and too far away from the Mexican population centers in the south to defend and manage adequately.

The end result was the Treaty of Guadalupe Hidalgo, signed on February 2, 1848, which officially ended the Mexican-American War and resulted in a massive territorial transfer to the United States. Guadalupe Hidalgo was a community just north of Mexico City.

Under the treaty, Mexico ceded over 500,000 square miles of land, including California, Arizona, New Mexico, Utah, Nevada, and parts of Colorado and Wyoming, in what became known as the Mexican Cession.

The Rio Grande was established as the official U.S.-Mexico border, resolving the Texas boundary dispute. In exchange, the U.S. paid Mexico $15 million and agreed to assume $3.25 million in debts owed by Mexico to American citizens.

Had Mexico at least met with John Slidell three years earlier, they might have wound up in basically the same place, but $7 million dollars richer, and without having gone to war and having been occupied.

This wasn’t the end of the territorial concessions. Just five years later, in 1853, U.S. ambassador to Mexico, James Gadsden, negotiated a land deal between the United States and Mexico, in which the U.S. bought 29,670 square miles of territory in present-day southern Arizona and southwestern New Mexico for $10 million. The purchase aimed to facilitate the construction of a southern transcontinental railroad and resolve lingering border disputes after the Mexican-American War.

Despite the importance of the Mexican-American war, most people have forgotten it because it was overshadowed by the much larger Civil War that came less than a decade later.

Yet a simple look at a map will tell you that it was the Mexican-American War, probably more than anything else, which has shaped the map of North America today.

The Executive Producer of Everything Everywhere Daily is Charles Daniel. The Associate Producers are Austin Oetken and Cameron Kieffer.

Today’s review comes from listener 2012 Road King Classic over on Apple Podcasts in the United States They write.

Love, love, love it!

I love this podcast! The variety of topics, coupled with the proper attention to detail without the host’s inclusion of personal opinion, is both welcomed and refreshing. Keep up the great work, Gary! As the newest member of the completionist club in North Carolina, I found the clubhouse in need of refreshments so I have filled the fridge with our local favorites: Cheerwine, Sun Drop, and plenty of BBQ. Nothing could be finer than to be in Carolina … unless you are a Panthers fan.

Thanks, Road King! I’d like to formally welcome you to the completionist club. Always nice to see the Tar Heels representing. As for the Panthers…..well, you always have college basketball.

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