The Mexican-American War
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After several years of rising tensions, on May 13, 1846, the United States Congress declared war on the nation of Mexico. The war only lasted two years and the conduct of the war was decidedly one-sided. The conclusion of the war, however, resulted in changes to both countries, which can still be seen on the map and felt on the ground today. Yet despite being one of the most important conflicts in the history of North America, it's been largely forgotten.

Learn more about the Mexican-American War, its causes, and its resolution on this episode of Everything Everywhere Daily. This podcast is brought to you in part by Stash.

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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 rather than the Mexicans to the south. The settlers in Texas, and 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 really started the United States and Mexico down the path to war was the vote by Congress to annex Texas and admit it to the Union on March 1, 1845. In response to the vote, the Mexicans removed their diplomats from the United States. One of the major issues was that Texas had said that their southern border was the Rio Grande River, and Mexico said that it was the Nueces River further north.

On March 4th, President James Polk took office, who was a big advocate of Texas joining the Union and of the United States 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 to purchase California.

However, the Mexican government 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 smaller 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 of 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 8th and then at the Battle of Rosaca de la Palma on May 9th. On May 13th, Congress declared war on Mexico, with President Polk claiming that, quote, 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 that if the United States was born of revolution, then they shouldn't be doing the exact same thing that the European powers did.

The Bear Flag Revolt was an uprising by American settlers in California against Mexican rule in June of 1846, during the early stages of the war. Inspired by the expansionist beliefs of manifest destiny and tensions over Mexico's control over the region, a group of settlers led by William Ide and John Fremont 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 the Bear Flag Revolt. However, the rebellion was short-lived, as U.S. naval forces took control of Monterey and San Francisco in July of 1846, officially placing California under U.S. military rule. The Bear Flag Republic lasted only a few weeks before California was absorbed into a U.S. territory.

In August 1846, General Stephen Kearney led the Army of the West into Santa Fe, New Mexico, facing no resistance, as Mexican Governor Manuel Armijo fled without a fight. Kearney 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 by the U.S. to push further into Mexico. With that decision, U.S. forces under General Zachary Taylor advanced into northern Mexico. The Battle of Monterrey took place from September 20th to September 24th, 1846. The city of Monterrey, a heavily fortified position defended by General Pedro de Amputia, 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. And there was a good reason for that. The United States had a huge advantage in almost every metric. Its population was three times that of Mexico's, and its economy was even larger. Despite this advantage in resources, however, the 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 U.S. army in terms of professionalism. Ulysses S. Grant, who served as an assistant quartermaster in the war, later wrote the following in his biography. Quote, "...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 own power than they were with fighting the United States.

The Battle of Buena Vista occurred on February 22nd and 23rd of 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. General 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, quote, tell him to go to hell. After intense fighting, the Mexican army suffered heavy losses and shortened 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 then began to march towards Mexico City, following roughly the same route that Hernan Cortes took over 300 years earlier. Scott gradually made his way towards Mexico City, fighting with the Mexicans who fought defensive battles to slow him down.

He won battles at Cerro Gordo in April, Contreras and Chorobusco 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 very little leverage. Their only option now was a guerrilla 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 when the war started. But now there was talk of annexing all of Mexico considering that they were occupying most of it. Oddly enough, while it was mostly Northerners 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 in the United States.

Both sides now had an incentive to come to the negotiating table. The Americans didn't want to be occupying Mexico any longer, as 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 in the North were lost. Texas had been gone for over a decade at this point, and California had its own rebellion and now 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 2nd, 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 and today is a neighborhood of Mexico City.

Under the treaty, Mexico ceded over half a million square miles of land, including California, Arizona, New Mexico, Utah, Nevada, as well as 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 may have wound up in basically the same place, but $7 million richer and without having gone to war and having been occupied.

And this wasn't the end of 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 United States 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, simply because it was overshadowed by the much larger civil war that came less than a decade later. Yet, a simple look at the 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 Okun and Cameron Kiefer.

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