Some Mexicans came to America, and for some, America came to them.
In 1836 the Republic of Texas separated from its previous Mexican rule. After spending the better part of their one sovereign decade attempting to join the United States, Texas was annexed by the USA in 1845. The United States offered Texas security, stable rule, and economic survivability, as many had families in the United States and feared that Mexico had plans to strike once more at Texas, hence this trope. The United States also would protect the settlers' right to own slaves — these settlers, first invited to Texas by the Mexican government after agreeing to follow Mexican law, balked at Mexico's ban on slavery in 1829, which these slave-owning settlers very much disagreed with. The new Texas immigrants from the United States became known as Texicans while the original Hispanic locals were called Tejanos. Texas was originally granted a one-year exemption from the 1829 ban, but Mexican president Anastasio Bustamante ordered that all slaves be freed in the law of April 6th, 1830 which also prevented further emigration to Texas from the United States and increased import taxes. This law didn't stop further immigration as Americans continued to settle Texas illegally. To circumvent the law, many Anglo colonists converted their slaves into indentured servants for life. The slavery aspect is something Texans unsurprisingly tend to gloss over when discussing their state's history. After Santa Anna overthrew president Anastasio Bustamante in 1832 the Mexican government started giving concessions to Texas that included a repeal on the emigration ban, more representation to Texas, and the right to trial by jury. However, Santa Anna had other plans as he overturned the 1824 constitution in 1835 and ordered all state legislatures and militias to be disbanded. The Tejano governor of Texas refused and when Mexican authorities attempted to seize a cannon used for defense against Comanche raiders it led to the Battle of Gonzales which sparked the Texas Revolution.
In 1846, the United States Congress declared war on Mexico following a border skirmish between a Mexican cavalry detachment and a U.S. patrol. Long story short, the US army fought all the way to Mexico City, Mexico lost the fight, and the Mexican government signed the Guadalupe-Hidalgo treaty, in which Mexico transferred to the USA the territories that are nowadays covered by California, Nevada, Utah, Arizona, New Mexico, and parts of Colorado and Oklahoma — that is, around 60% of its territory (though only a very small part of its population or gross national income) — in exchange for the sum of 15 million dollars (accounting for inflation, that's about $390 million in 2012). This was later followed by the sale of La Mesilla / purchase of Gadsden for the purpose of building a transcontinental railroad.
Needless to say, the thought of being formerly such a huge country that lost so much land supposedly means that every single Mexican has at one point dreamed of getting back the "Lost Territories". And of course, Mexico being next to the U.S. a crapsack world by comparison, this desire is all but a pipe dream. There is a truth in television aspect here, as activist groups like La Raza and MEChA have stated in their charters the goal of bringing back to Mexico much of its former land.
But what if, in fiction, the USA were weakened enough to make this dream come true?
Thus, whenever in speculative fiction you see the United States somehow greatly weakened, or in the past before the USA became a superpower, you can pretty much be assured the back story will involve Mexico invading and conquering at least Texas and California. This is particularly ironic, because Mexico's economy right now is smaller than both Texas and California.note ; in fact should Mexico hypothetically succeed this very moment in recovering just these two states, the Mexican economy would practically quadruple its size. But then again, it IS Texas.
- The above picture comes from an ad for Absolut vodka (a Swedish product) that only ran in Mexico. To say that there was a bit of backlash when it was leaked into the USA is putting it mildly.
- In Red Dawn (1984) Nicaragua and Communist Cuba invaded the US through Mexico after a limited nuclear strike.
- In the Wild Wild West movie, Mexico was one of the backers of Loveless's plan in exchange for the return of Texas, New Mexico, Arizona, and California. That's right, along existing state borders, not the pre-1848 one.
- Referenced in 80s Cannon-produced action film Avenging Force. The lead white supremacist's rant about liberals and communists refers to 20 million Mexicans in the United States who would just "love to rebel and join the Socialist Republic of Mexico."
- In the comedy Viva Max!, the eponymous General Maximillian is driven to near insanity when the Mexican woman he has a crush on spurns him and insults his capacity as a military officer. He assumes that, naturally, the best way to impress her is to recapture the Alamo.
- A news story near the beginning of RoboCop (1987) describes rebels in Mexico rattling the U.S. borders.
- In Escape from L.A., all of Latin America has been united under the Shining Path and is about to invade the US. Revolutionary agent Cuervo Jones kidnaps and brainwashes the President's daughter in order to seize control of the "Sword of Damocles" EMP satellite superweapon, and plans to use it to lead off the war. Snake Plissken is sent into the ruins of Los Angeles in order to retrieve the weapon and stop the invasion.
- In the book One Second After (taking place in the aftermath of an EMP attack on the US) taking advantage of the confusion, Mexico takes over a good portion of the southern US, including Texas.
- The War Against the Chtorr. Southern Mexico provides staging areas for an "Army of Economic Liberation" to invade an ostensibly demilitarised United States. The invaders get their ass handed to them due to secret technology the US has been hiding. When Mexico subsequently collapses, many other nations think it's not a coincidence.
- Inverted in It Can't Happen Here. The Windrip regime invades Mexico as a means of spreading its empire and encouraging patriotism among the masses. Played with in that the regime falsely claims Mexico attacked America as justification for the war.
- In 1920: America's Great War, Imperial Germany defeated France in 1914 and the war never exploded into World War I. In 1920 Germany has allied itself with Mexico and a weak US government has not been able to prevent them from shipping a small army over to Mexico. With the US army undermanned and under equipped and with President Woodrow Wilson incapacitated due to a stroke, Germany and Mexico launch an invasion of the US. The Mexican army invades Texas and a German army invades California. Despite initial successes, it becomes clear that a conquest of Texas is impossible due to the logistics and the real goal of the invasion is California. With the rail road lines sabotaged and the German Navy's control of the sea, California is cut off from reinforcements and if the Germans can manage to take San Francisco they will be very hard to dislodge. The Germans assume that the US will accept the loss of California and sue for peace rather than fighting a long war of attrition to regain it.
- The epilogue to Star Carrier: Deep Space reveals that, as Earth enters its sixth world war, Mexico (along with Honduras) has seceded from the United States of North America and invaded California and Texas.
- George Friedman, in his novel The Next 100 Years, details his very broad political predictions for the 21st century and states that Mexico will at least attempt this by 2100, due to Mexico's likely stabilization (he points out China has been in chaos in the recent past and overcome that chaos), its population growth and the US population decline.
- Since Victoria chronicles the downfall of the United States and the rise of the American successor states, this is present:
- As America declines and the corrupt Federal Government comes to depend more and more on minorities to support its ruthless rule, President Warner eventually agrees with Mexican nationalist leaders to establish a condominium over Texas, Arizona and Newmex. This backfires, however, as the locals rebel, and end up destroying most of the Mexican army in the ensuing war. The resultant power vacuum then allows the Aztecs to seize power in Mexico itself.
- Another, roughly concurrent civil war in California sees that state split. The Hispanic-dominated southern part is apparently annexed by the Mexicans, whereas the north becomes a transhumanist, culturally homosexual Silicon Valley state.
- Chase: In the episode Repo the criminal they are chasing is a believes that America stole the territory and doesn't believe in the authority of the police, making comments about it to most people he meets.
- Revolution: Mexico seems to have weathered the Blackout a bit better than the US and is considered a serious threat to an independent Texas. With 70% of its troops stationed on the Texas-Mexico border, Texas stays out of the war between the Monroe Republic and the Georgia Federation and is later eager to make peace with the emergent Patriots. Based on a map shown in season 1 Mexico does seem to have lost Baja to an independent California but this is not explored.
- Sliders: One episode featured a world where Mexico decides to take back Texas and California (possibly others as well). They get quickly thrown out of Texas, however, since "every Texas citizen owns a gun", but California cities turn into war zones.
- In Shadowrun, Aztlan (AKA The Country Formerly Known As Mexico) invaded and conquered parts of California and Texas (both of which had split off from the U.S.).
- Twilight2000. After the Soviet nuclear attack on the U.S. in 1998, Mexico invaded the southern U.S.
- Its spiritual sequel 2300 AD had Mexico still holding Los Angeles, Arizona, and New Mexico, but not Texas.
- Inverted in GURPS Cyberworld: the US occupies much of Mexico (though there are still border controls in place to keep Mexican third-class citizens from traveling to the "Upper 48").
- Mexico attempts to take Texas (claiming it belonged to them, even if they were centuries late) at one point in the Deus Ex Back Story, after the incident with the original NSF reveals how weak the US had become. It's not mentioned in the main plot, but it is given through in-game media. The Nameless Mod mentions it in the fan fiction shop.
- A Mexican-occupied Texas level was planned, but cut from development.
- Soviet troops in Red Alert 2 invade via Mexico (or at least we see a Apocalypse Tank crushing a "Welcome to Texas" sign).
- The backstory states that Mexico is part of the World Socialist League, and the USSR faked a civil war there to justify a troop intervention — which provided them a base to invade the USA.
- In Tom Clancy's HAWX, the eponymous squadron flies to Ciudad Juarez due to Mexican rebels going into the United States to escape retribution from government forces.
- A common conflict in the Alternate History grand strategy game Victoria: An Empire Under the Sun. Incidentally, its main scenario starts with an independent Texas at war with Mexico due to Author Appeal.
- In the Kaiserreich mod for Darkest Hour, if the Second American Civil War breaks out Mexico has the option of seizing the opportunity to try and reclaim the lost border territories.
- Inverted in xkcd; a handful of satellite operators debating the situation with Israel and Palestine when the sat is scheduled for a check-in over that general area get shut down by their boss changing the coordinates to Oklahoma, which another technician calls "Occupied North Texas". Leading to the boss sighing and just telling him to shut up.
- The Nation of Aztlan movement has this as its goal. While there has been greater awareness of Mexican heritage (and Hispanic heritage in general) starting from around the 1960's, political separation (as in joining Mexico or forming a new country) is not taken seriously by anyone except fanatics (both for and against).
- Imperial Germany during World War I delivered the Zimmermann Telegram, which offered to give Arizona, New Mexico and Texas to Mexico if it sided with Germany. The British decrypted the message and sent it to the U.S. before the Mexicans could even get around to responding. This was pretty much the last straw that drove the U.S. to enter the war against Germany. After actually receiving the Zimmerman Note, Mexican President Carranza had the Mexican Army's General Staff analyze it and what Germany was offering, and turned down the offer on the grounds that 1) holding and occupying the states in question would have been a nightmare; 2) German financial assistance was meaningless in that the only country capable of supplying Mexico enough arms to attack the United States was the United States itself! and 3) No German military assistance was immediately forthcoming due to Germany's own situation in Europe and Allied shipping patrols in the Atlantic. Carranza correctly concluded that the Zimmerman Note was a case of Germany saying to Mexico "Let's You and Him Fight" in an effort to keep the U.S. out of World War I.
- Inverted by the suggestion that Tamaulipas, Coahuila, and Nuevo León would be on the shortlist of Mexican states to join the U.S., being closer to Texas than the rest of Mexico. Also, as recently as the 1980s the annexation of Baja California was proposed as a means of alleviating Mexico's foreign debt owed to the United States.
- The annexation of the entirety of Mexico was actually a consideration in the aftermath of the Mexican-American War, but domestic political disputes (ie slavery) put an end to that idea. Many in the South worried that this would result millions of new, non-white US citizens while in the North it was worried that this would create additional slave states and tilt the Senate's balance decisively in favor of preserving slavery.
- The Gadsden Purchase would severely complicate any attempts to reacquire the former territories of Mexico through legal means. This bit of land forms the entirety of the US Mexico border of the states of Arizona and New Mexico. Unlike the rest it was purchased through legal means without the context of war or exploitation. If they wanted it back it would become Russia Called; They Want Alaska Back.
- Most of the brief history of the Republic of Texas involved fending off various attempts by the Mexican government to retake Texas, including a number of land invasions and naval battles (including a brief alliance between the Republic of Texas and the Republic of Yucatan, another state which had seceeded from Mexico). This period of conflict led directly into the Mexican-American War after the expanding United States finally agreed to annex Texas.
- A most recent example: In 2006 after losing the presidential election of Mexico, former candidate Andres Manuel Lopez Obrador, submitted a lawsuit against the U.S. to the International Court of Justice in Hague, demanding the return of the California, Nevada, Arizona, Utah, New Mexico, and Texas territories to Mexico, alongside with reparations for the Mexican-American war. It's unlikely it will prosper (particularly given that the ICJ can only hear a case if both parties to the dispute agree to their mediation), but still...
- A variation is taking place in Eastern Europe. Russia called, they want Crimea back...
- During the Cold War, due to the fact Germany's eastern border wasn't definitively fixed, The Bonn Republic was making the following sentence resume its policy toward the East : Germany called, they want the Ostgebiete back. This ended after the end of the Cold War, by which Germany recognized the borders and abandoned its claim to Eastern territories. This has also become moot with the European Union and the Schengen Visa allowing Germans to travel back to their ancestral homes in Silesia and Pomerania.
- During the interbellum, it was "Hungary called, they want Transylvania back."
- In the run-up to World War I, it was very much France won't stop calling and they want Alsace-Lorraine back very much.
- The road to World War II started with "Germany called, they'd like to remilitarize the Rhineland." Then it was "Germany called, they want to annex Austria." And then it was "Germany called, they want the Sudetenland back". And then it was "Germany called, they want Memel back and the rest of Czechoslovakia, thank you very much." And finally, it was "Germany called, they want Danzig and the Polish Corridor back", at which point the rest of the world told them to shut up and stop calling. They did not.
- It is rumoured that the undeclared reason why the British Army was sent into Northern Ireland in 1969 was to forestall any attempt by the Irish Republic to move its military forces into the predominantly Catholic border counties, in order to preserve peace and prevent ethnic cleansing of Roman Catholics by Protestants. (And incidentally to reinforce the Republic's claim to sovereignty over the whole island of Ireland - you could read this as "Dublin called - we want the Six Counties Back".) It is known the Republic mobilised its armed forces, including reservists, and sent them North in the summer of 1969 to answer the emergency. Informed opinion is that South Armagh, County Tyrone and County Derry would have been occupied for peacekeeping and humanitarian reasons (but the Prot areas would have been left for the British to deal with as their problem).