The US is a major problem here since they won't tolerate a competitor for hegemony in the Western Hemisphere. I'd suggest a successful CSA to nerf them, but I am so sick to death of successful CSA's in alternate history that I can't recommend doing yet another (I swear to god, if it's not the biggest AH cliche out there, it's at least in the top three...and they all ignore the myriad economic, social and political problems that relegate a viable Confederate nation-state to the realm of ASB). Instead of that, I'd suggest a close examination of US involvement in Latin America (I'm no expert on the early years, I'm afraid), to see whether it can be diminished or diverted elsewhere, or else whether the USA and Mexico can reach an understanding regarding spheres of influence, leaving Mexico to deal with Guatamala and whatever else you had in mind. That actually seems a bit more interesting than just "Ameriscrew, and see who's left to pick up the pieces!"
ok what about a world where there never was a Monroe Doctrine & the US has just gotten, temporary at least, humbled by a Anglo-Mexican Alliance?
The issue is that the OTL Monroe Doctrine was enforced by Britain in order to keep its European rivals out of Latin America...in order to butterfly that, you may have to butterfly the Peninsular War...which would in turn have considerable effects on Mexican independence. Again, I'm not terribly knowledgeable about this period, so someone else around here will likely give you more detailed ideas. That said, the more I think about this, the more a POD around 1810 seems necessary. A UK more at odds with the US would be easier to achieve with some chicanery involving the War of 1812, after all.
but the Monroe Doctrine was an American thing that Britain just backed. Plus even if that is the case if its Mexico doing it then its not in violation of the Monroe Doctrine
ok I had this idea to put in a TL that I am writing for sometime between the 1850's & 1880's have Mexico decide to reconquer Central America & succeed at least with Guatemala for a couple decades. What I was wanting to know is how possible this is with an at least somewhat improved military? And what would the reaction be of the rest of the world?
but there never was anything resembling a Monroe Doctrine ITTL that i am writing.Right, but the British will still back it as long as it suits their interests, and it suits their interests as long as the Spanish colonial grip is broken, since they can horn in on Latin American markets and use the Doctrine as an excuse to keep the French or whoever else out. That's why you need to go back to when the Spain was still in charge, to muddy up something involving Spain or the US-UK relationship or both. Otherwise, OTL ensues.
While we're at it, it's worth noting the geography of Mexico makes it hard for the central government to consistently assert authority beyond the Mexican Plateau. That's not insurmountable, but it's worth noting since it puts Mexico at a disadvantage in a conflict with the US over Texas or California.
How are you dealing with reality?
Mexican instability after independence, Reform War, French Intervention, etc?
Best,
ITTL when the US lost to the UK & Mexico the US acquired all of Mexico's debt owed to it & most of it owed to Britain, Alta California south of the 36 30 parallel (the rest was taken in a US intervention during Texas Revolution), & Texas south of the Nueces & west of the Pecos. Mexico is not fully stable but a lot more (as of the mid 1850s anyway) than OTL & as for the French intervention i am not planning on it happening.
my plans also were to have a British & possibly later on French military mission to Mexico reforming & modernizing its army a lot & its navy somewhat
Starting with Diaz in the 1870s-80s, maybe.
Best,