Mexico annexed after 1848

[ag]

This question periodically arises, and I once gave what I believe would have been the oucome: the US would not have survived the Civil War as a single entity. I guess, by 1880 the map of North America would have  looked something like this: a huge (still British) Canada (including Alaska, Washington, Oregon, and a substantially more southerly border from there eastwards), the rump USA (Northeast and Midwest, possibly without Maryland and Delaware), CSA - the South + Maryland/Delaware and parts of southern Midwest + NE Mexico, California (including the entire Mexican NW, Arizona, New Mexico, etc.) and rump Mexico.

The reason I think this would have been the case is that annexation of Mexican heatland would create an extremely unstable situation, with three irreconcilable territorial entities uneasily united under a single government. Remember, Mexican heartland at that stage is densely populated and largely lawless even aside from the US invasion, while Mexican population is hostile to the Protestant Anglo invaders.  Assimilating this area by colonisation is impossible in the short term. The Mexican-American war would have gradually passed into a guerilla stage, with the US government control within Mexican heartland limited to actively occupied urban areas. While colonisation of the sparsely populated Northern Mexico would not be a problem by itself, it would create new problems elsewhere, since Tamaulipas, Coahuila and parts of Nuevo Leon would easily develop into new slave states, strengthening the South, increasing the unhappiness of the North. Some resolution would have to be found before they join the US as states - meaning likely earlier start of the Civil War. When hostilities would break out between the North and South, most of the Union army would find itself posted in Mexico, trying to control the guerilla. Both North and South would be tempted (in fact, would find it indispensible) to appeal for the support of the Mexicans, but the price of that support would inevitably be the recognition of Mexican independence.  The Southerners, being secessionist themselves, would find themselves readier to do this, meaning that the Union troups would find themselves attacked  on both sides as they try to retreat to join the battle.  Most likely, the Southern secession would succeed. US would find it extremely difficult to have a meaningful link with California, etc. suggesting a possible secession there as well.  Mexico would thus regain its independence, though in much abridged form (probably less than half of its current area, though most of its population), with the North split between California and CSA (or, possibly, some sort of an independent Texas state, separate from the CSA).  Of course, nobody would expect that Britain wouldn't react to the disappearance of a strong US by trying to extend its Canadian holdings (and it wouldn't find much effective opposition frome the defeated rump USA).

In the extremely unlikely case that the enlarged US would survive, it would be a dramatically different country. In 1848 Mexico's population is nearly half of that of the US. By the early 1900s the combined country would have a Catholic majority, implying a radically different politics (expect few if any Protestants ever elected President from 1900 on). The Mexican heartland (roughly from Guadalajara-Aguascalientes-Leon-Tampico line further south) would continue being substantially separate both culturally and politically, dominated by some sort of a local political party. The country would be very different both from today's Mexico and the US.

[ag]

Mexico had only 1/3 of the US's population in 1848. Sure its 19th century rate of population growth woudl be larger than our timeline but you forget that mexico would be in a first world nation so it wouldn't grow as much as it did in our 21st century(instead of 110 million mexicans plus 20 million more in the US making 130 mexicans we'd see abotu 1/2 of that). We'd have about 70 million mexican-americans in that timeline. Thanks to air conditioning/demand for labor we'd see mexicans move north like how the blacks did so only about 30-40 million mexicans in the mexican states

Except, of course, that for the first hundred years after 1848 the natural growth rate in the US was far, far higher than in Mexico. Assuming, as you do, that Mexico would become "first world" (meaningless in the 19th century, but I take this to mean "like the US") after 1848, means assuming a much higher population growth rate among the hispanics. In 1900, the average life expectancy at birth in Mexico City was about 20-24 years. I believe it was over 40 years in the US. No fertility rate (and it wasn't higher in Mexico than in the US, anyway) would make up the difference.

You seem unaware of the basic fact, that extremely poor countries do not necessarily have large population growth. Most population growth occurs at the transition to development, which you imply, would have occured far earlier in Mexico than it did. For much of human existence, the high fertility rates were balanced by high death rates, meaning that population was stationary. Then, with mortality rates falling, the fertility rates lag behind, resulting in a population explosion over a couple of generations. If anything, these days the catch-up happens faster.  In Mexico it took barely a generation: 30 years ago Mexican women had 7 kids, today the fertility rates in Mexico and in the US are the same, at roughly 2.1 per woman.  I believe, the comparable fertility drop-off in the US took over 50 years. If the transition happened in Mexico at the same time and at the same rate as in the US, there would be many more (in fact, several times more) Mexicans in 1900 than there actually were, not fewer.

[ag]

Mexico had only 1/3 of the US's population in 1848. Sure its 19th century rate of population growth woudl be larger than our timeline but you forget that mexico would be in a first world nation so it wouldn't grow as much as it did in our 21st century(instead of 110 million mexicans plus 20 million more in the US making 130 mexicans we'd see abotu 1/2 of that). We'd have about 70 million mexican-americans in that timeline. Thanks to air conditioning/demand for labor we'd see mexicans move north like how the blacks did so only about 30-40 million mexicans in the mexican states

Adding to what I just wrote. Talking about air-conditioning and the timeline to the 21st century is meaningless here. I have a hard time believing the combined state would have survived past 1870. Even if it did, it would have been radically different from the real US already by 1900. The key to my argument is that it would be extremely hard for the US to digest the Mexican heartland over the next few decades, implying an extremely unstable political configuration.

No massive migration of the Protestant Anglos into the Mexican heartland would be possible, unless the area was pacified, which I do not see happening, at least, for a couple of decades. Unlike all the other US conquests in the 19th century, the Mexican heartland was densely populated by the standards of the time - there was no space for the same type of settlement as happened along the Western frontier (unless, of course, the US government was willing to physically exterminate, say, three quarters of the local population, including the white hispanic community - which would be considered barbaric even by the sad standards of the period).

There was a reason even Polk never proposed annexing entire Mexico. What he wanted to do is to annex the North - say, 60% of the remaining Mexican territory, which only had a small proportion of the population. The reason he didn't do it (he could always disregard whatever his ambassador signed with representatives of some fleeing interim Mexican government of dubious legitimacy) is internal US politics. Annexation of such areas as Tamaulipas, Coahila, etc. was entirely unacceptable to the Northern politicians, since it would imply a sharp power shift towards the South.  In practice, the Northern Senators would have simply blocked the ratification of any such treaty. Had they yielded, chances are the secession would have happened earlier than it did - but it would have been the secession of the North. In case it were unsuccessful, the resultant South-dominated US would have resembled more modern Brasil, than it actual self - it would have never become the industrial powerhouse it did, it would remain dominated by plantation farming for decades to come. By the way, since plantation farming required less white labor, the European migration would have gone to Argentina to a much greater extent than it actually did.

Of course, the Mexico proper would have been anti-slave, and this would have made the complete gobbling up of Mexico on paper more acceptable to the North than the partial dismemberment I have just discussed. But the annexation of the entire Mexico presented different problems, that were much more apparent even at the time, and this is why this was never seriously contemplated. Even assuming US could somehow disenfranchise the pure-blooded Indians (over a half of Mexican population at the time), the remaining "ladino" population would still be sufficiently numerous to dominate local politics for generations to come (in fact, as I discuss in another post here, by 1900 it would have been larger than it was if the US project were to succeed). Furthermore, assuming this population agreed to participate in US politics (again, an optimistic assumption - I actually foresee a lengthy guerilla warfare ensuing) it would have likely formed an alliance with existing Catholic communities in the US proper (remember that quite a few of the Irish US soldiers sent to fight in that war defected to the Mexican side - enough of them to form the Batalion de San Patricio, which, until its defeat in battle and execution of its members formed one of the better Mexican fighting units). This would present a sizeable force in the US politics.

From this, assuming the extremely unlikely case the US is still around for more than 15 years after Mexican annexation, I see one of the two possible developments (and, without the benefit of hindsite, it seems the US politicians at the time had some vague idea of the same): either one of the two major US parties becomes a de facto Mexican/Catholic party (and, given the forthcoming German/Italian/Irish immigration, this becomes the dominant party by 1900), or, and I think this would be more likely, the Mexican states (again, by that time only the states south of the Guadalajara - Tampico line would be still properly Mexican, but they would have had substantially larger population than they actually had, due to the lower mortality and consequently higher population growth) would become the province of some sort of an autonomist "Partido Mexicano" or "Partido Hispano", with other parties only active in the Anglo states. This, in turn, would have a de facto impact of eliminating the popular election of the President: assuming there are still two Anglo parties, no party would be able to get an electoral majority. The election would be routinely decided in Congress, and, in practice, it would come from the negotiation between the party leaderships.

To sum up, assuming the what I believe to be an extremely unlikely eventuality of US successfully annexing Mexico and not disintegrating in the process, the US internal politics would be radically transformed and made dependent, to a substantial degree, on the preferences of the Mexican heartland. This was recognized at the time, and for that reason there was not serious discussion of annexing Mexican heartland. The proposals to that effect that were introduced were designed to sabotage the more limited annexation of the largely empty Mexican provinces beyond what actually was annexed.

The only parts of Mexico that could have been plausibly annexed and digested at the time were Baja California and, possibly, the rest of the Northwest (Sonora, parts of Chihuahua, may be Sinaloa and Nayarit, Durango etc.). I guess, nobody really wanted all that desert.

[ag]

That's quite interesting what you mentioned ag that the annexation of more area in Northern Mexico could have lead to a major shift to a southern power base. So the US becomes Brazil-like with the South like poor Northern Brazil and New England and the Midwest like richer Southern Brazil. What would we have in that inventuality? An Argentine superpower as Argentina gains a large number of the immigrants that would have gone to the United States? That to me sounds incredibly interesting. Of course Argentina would have to keep its internal political order to accomplish remaining a first world nation.

Given that US plantation-dominated economy in this case does not require as much labor as it actually did, and that in general US is less attractive for European migration, I guess, it could be plausibly argued that Argentina also gets a lot more of these immigrants, and, consequently, possibly different domestic policy. But I don't know enough about Argentina to do even educated guesses here.