Mexican-American War

""Remember the Alamo!" Wait, that was the previous war."

The year is 1846. The Southern United States' plantation economy is becoming less and less practical as Europe gets more of its cotton from other sources, particularly India and to a lesser extent Egypt. Industry is driving more and more people north, and the balance between free and slave states is rapidly shifting. This only increases when the Oregon Territory is annexed. The answer: build a railroad from New Orleans to the Pacific coast, where many American expatriates already live. But the land in between is in the hands of a hostile Mexican government...

Meanwhile, European powers are developing spheres of influence in China, and the US government finds itself in need of a large Pacific port, and there's a big one in the Mexican province of Alta California, which everyone knows is much more valuable than the newly-annexed Texas. Unfortunately, relations with the British Empire are tense and there's a great fear that this will be their next conquest.

The answer? War, of course!

Lasting from 1846-1848, the Mexican American War was fought between the United States and Mexico over a small land dispute in Texas. Despite its small origins, it eventually resulted in the invasion of Mexico. Though the war is seldom depicted in contemporary media, both the United States and Mexico as we know them exist, in part, as a result of this war.

Tropes from this time period include:

 * Awesome McCoolname: Don Benito Wilson, which means "Lord Benedict" in Spanish.
 * Child Soldiers: Los Niños Héroes.
 * Altough documentary evidence is scant regarding their actual existence.
 * Defector From Decadence: Happened on both sides.
 * On the American side, there was Saint Patrick's Battalion, a majority-Catholic group of soldiers who defected from the US Army to side with Mexico.
 * Also, several Mexican leaders defected to the US, primarily due to their disgust at Santa Anna's dictatorship and the poor logistics due to corruption.
 * Divided States of America: California was briefly a separate country early in the war.
 * Eagle Land: The war was a part of Manifest Destiny -- to stretch the United States from shore to shore.
 * Expanded States of America: The United States ended up annexing half of Mexico.
 * Four-Star Badass: Both Zachary Taylor and Winfield Scott won every battle they fought.
 * Final Battle: The Battle of Chapultepec.
 * Hatedom: Decried by many, such as congressman Abraham Lincoln, as an attempt to expand slavery. It didn't help that the war's biggest proponents were politicians from the slave states.
 * There's not a lot of Mexicans who like how it ended.
 * A few Americans didn't like it either, as it led into The American Civil War.
 * Plus many Americans expected annexation of the entire Mexican territory, not just half.
 * Hey, It's That Guy!: Lieutenant Ulysses S Grant served under General Zachary Taylor. Both would later be US Presidents. Other people involved include Jefferson Davis, Kit Carson, John C. Fremont.
 * Also Robert E. Lee, Winfield Scott, George Meade, and dozens of other Generals and high-ranking officers of the Civil War. Those who served as Lieutenants and Captains in Mexico were called up for their experience to fight fifteen years later as Generals in their own back yards of Virginia, Tennessee, Mississippi, Alabama, Georgia, Maryland, Pennsylvania, Missouri...
 * Abraham Lincoln was with the group of congressional Whigs who opposed the war. His record on his anti-slavery position during the war helped win the Republican nomination in 1860 for the Presidency.
 * Humiliation Conga: The Mexicans suffered military defeat after defeat, most of them routs (except for The Battle of Monterrey, which the Americans still won). And once the fighting was over, Mexico was forced to sign over half its land (including California), some of which was prime real estate (especially the parts with gold).
 * The war also left Mexico indebted to European powers which led to France's attempt in the 1860s to invade as part of Napoleon III's plan for empire. When the Mexican Republic fought back and crushed the fledgling empire, that was the end of the humiliation.
 * This war marked the Mexican "National character", which made Mexicans extremely pessimistic, distrustful of others, guided by Murphy's Law and resigned to their fate "because that's how it is in Mexico", and only today is beginning to be called an Old, senseless Mindset.
 * Jerkass: Antonio Lopez de Santa Anna. Exiled after his defeat at the hands of the Republic of Texas, Santa Anna offered the Mexican government his military 'experience'. Needing generals, President Farias accepted the offer... not knowing that Santa Anna had been secretly dealing with the United States to quickly end the war and give all contested land to the US. Once in charge of the army, he reneged on both deals by proclaiming himself President again and refusing to deal any further with the United States. He proceeded to mismanage the Mexican forces into a humiliating defeat.
 * Also qualifies him for Butt Monkey status, as Santa Anna is routinely listed by military historians as one of the worst generals ever.
 * Not to mention that the In-fighting between the Conservatives and Liberals made fighting much more inefficient in Mexico
 * Laser-Guided Karma: By adding so much western territory with this war's victory, especially lands south of the Missouri line that limited slavery's expansion, it heated up the slavery debate between North and South and became a prelude to the The American Civil War.
 * The swift resolution of the Mexican War convinced American military leaders in 1860-61 that the Civil War would be quick and relatively bloodless. Four years and 600,000 casualties later...
 * Santa Ana, please pick up the white courtesy phone..
 * Los Angeles: Beseiged for six weeks, it was the only American defeat in the California campaign.
 * The Americans recovered enough to defeat the defenders in a later battle, which ended the California campaign.
 * Mexico Called They Want Texas Back: This is why.
 * Never Live It Down: The war is still a very controversial topic in Mexico.
 * Nice Job Breaking It, Hero: When Zachary Taylor (Whig) won early victories that made him an attractive future Presidential candidate, the Democrat President Polk held him back by sending Winfield Scott (another Whig) to finish off the war in Mexico. It didn't work: Taylor won the Presidency as a Whig after a primary against Scott in 1848. And Scott's war heroism made him invaluable as a Union leader at the start of the Civil War (it was Scott's Anaconda Plan that helped win the war).
 * Starting a war to define the Texas border to the Rio Grande, President Polk? You end up with expanding the United States with a massive land grab that exacerbates the slavery debate into a bloody civil war within fifteen years. Yeah, good plan...
 * Nice Hat: Those big, feathered American officer's hats.
 * The Plan: Though there is little evidence to support this, it is believed that the war was begun by the Americans so they could take California before the British could.
 * The war occurred as the United States was arguing with the British (in control of Canada) and the Russians over the northern border of the Oregon Territories. By comparison, Polk negotiated a peaceful resolution on the Canadian border, which upset those who wanted to fight and get all of British Colombia
 * Our Presidents Are Different:
 * President Action: Say what you will about James K Polk, but he succeeded in getting what he wanted.
 * Polk is in fact to this day the ONLY U.S. President to keep every one of his campaign pledges (admittedly, there were only four or five).
 * President Buffoon: Antonio Lopez de Santa Anna, who managed to lose the Southwest, the part of Texas up to the Rio Grande, and (in an unrelated case) Guatemala during his presidency.
 * Prequel: To The American Civil War and The Wild West. Many military leaders on both sides of the Civil War sharpened their teeth here.
 * Sequel: In many ways, to the Texas Revolution, which occurred in the previous decade, and featured some of the same players, particularly Santa Anna. Also, when this war broke out, the governments of Mexico and the United States still had not agreed exactly on what the borders of Texas were.
 * Pretext for War: Polk sent an expedition from Texas, which Mexico still claimed, across the Nueces River into an area that both Mexico and Texas had claimed (the area between the Nueces and Rio Grande). When Mexican soldiers shot at Americans for "invading their country", Polk claimed that American blood had been shed on American soil, and got his war.
 * Protest Song: "Once to Every Man And Nation", written by abolitionist James R. Lowell in protest of the war. Also can count as Crowning Music of Awesome.
 * San Francisco: Captured peacefully and without struggle. Everybody goes out for beer to celebrate. This is not made up.
 * Shout-Out: The line in the Marines' Hymn, "From the halls of Montezuma...," refer to their contributions in this war.
 * Southern Gentleman: Don Benito Wilson.
 * Tear Jerker: Los Niños Héroes.
 * We ARE Struggling Together!: The vicious political infighting in Mexico and unwillingness to fight from the Mexican army were amongst the causes of their defeat. There was also some political divisions in the United States, but the superior training that the U.S. army had made up for it.

=== Depictions in fiction ===