54'40 and fight- The U.S. loses ~ but how?

[Midas]

Some of you may have glanced over I've posted quite a few threads about Canada over the past while. I'm trying to do a three-part TL that explores the development of Canada with three divergences from roughly the same set of early PoDs (one more different), mostly as a personal pet project. The two I'm focusing on here ultimately begin with a few minor alterations to the Louisiana territory (it becomes more 'frenchified' with refugees from the Vendée Rebellions which causes the eventual state to be somewhat like an American Quebec, though nowhere near the same linguistic homogeneity) culminating with a more favorable Treaty of 1818 regarding Canada (Red River territory, Upper Peninsula given to Canada, most of Lake Champlain in Canadian hands (as far south as Ticonderoga), 44th parallel is the dividing point between NY/Canada, 48th parallel west of there the temporary border to be re-determined at a future time). I'm going to hand-waive this PoD causing any major changes to history during this point- it's a stretch with some of the significant changes described here, but I want a recognizable TL and am less interested in politics outside the Americas until the 1870s+. So this means that Polk has the presidency, same congressmen/senate composition etc.

The PoD for the 54'40 War here is set in April of 1845 (around the 24th). The United States has just approved the annexation of Texas and will likely be going to war with Mexico in a few days. For whatever reason (find me one!) the United States Senate approves a hostile resolution claiming the whole Oregon territory as United States territory that brings about a war between Britain and the U.S.

Unfortunately, I don't really know what this "hostile" resolution consists of and how it brings the United Kingdom and United States to war, but that's what I'm aiming to do. I do think the war is a disastrous defeat for the United States (I can be convinced otherwise though I suppose). The territorial changes I anticipate in the Peace Treaty look like:

• The border of the United Kingdom/United States follows the lower Columbia river and extends eastward along the 46th parallel (following the OTL Washington/Oregon border, but extending eastward along the 46th).
• At the easternmost edge of the Red River Territory (along the 46th parallel) the lands down the Mississippi to the 45th and then east to Upper Michigan Peninsula are ceded to Britain/Canada.
• All of Maine east of the Penobscot River is ceded to Britain/Canada.

That's how I'd like it to end; but I want to know how it goes, and I'm looking for people more knowledgeable and with outside insight to tell me how the war might look and how this peace treaty could come about. In the future I'd like the U.S. to take Mexican territory (this TL is a bit of an Ameriwank/Canadawank), so any suggestions on how that might come about would be appreciated. I'm open to (and greatly encourage) suggestions on future implications of the war and the peace treaty on Canada/U.S. and Mexico as well. I'll probably necro an older thread I posted with more specific borders, incase anyone has any more insight on how cities/states in Canada/U.S. will develop differently.

I plan on plugging this into material into a few fake wiki-style articles at some point to stylize the TL's happenings. If anyone cares, the other PoD is where the 54'40 war does not happen (a more populous/prosperous Canada along the 48th parallel, but one that is just a tad more buff than OTL Canada). I don't need much help with that and already have most of it fleshed out.

 

[KingByng]

A reason why the Yanks make the 54'40 hostile declaration seems simple enough: naked imperialism. The Treaty of 1818 gets seen in a "Brits stole our God-given land!" light in the decades after the treaty signing, and as a result there is a greater anti-British sentiment in the American people. As a reaction to that, Congress, in a hawkish mood over Texas, passes a resolution stating all of Oregon is theirs, and that eventually so will all of Canada. That last part isn't received well in London, and so British arms and supplies start finding their way into Mexican hands. This, in turn, is seen by the Yanks as an a violation of the Monroe Doctrine and war is declared.

As for how the war goes, it's now a two-front affair for the Yankees, and one front just so happens to be against the global superpower. So it isn't going to end well for the US. The Royal Navy, in several engagements, reduces the USN to not much more than a handful of ships, leaving large gaps in coastal defence for the British to make amphibious landings on. These landings would come as a supplement to the main invasion force that moves down from Lower Canada, with thrusts at New York, Boston, and Philadelphia. A smaller, secondary force in Upper Canada spends most of its time in a see-saw with USA troops (Detroit is taken, then lost, then taken, etc), but this is mostly a sideshow as most of the USA's troops will either be defending the much more important areas in NY, PA, and MA, or fighting Mexico.

The British regulars turn out to be of superior quality to the Yanks, who haven't fielded large armies since 1815. At year's end the British have taken New York, have Boston under siege, and have been drawing near to Philly. Combined with British supported Mexican victories in the south, Congress sees the writing on the wall and sues for peace. Since a lot of the North is under British control, the Yanks can't help but concede to British demands at the peace table, leading to your desired border. Mexico also receives a favourable settlement.

Now, in the aftermath of the war the public in the US get overcome with irredentist fever. However, as the war showed, they can't take on both Mexico and the UK at once, so they focus all their energies on "getting back" at the Mexicans (Mexico being the weaker of the two Allied Powers). After a while, US animosity towards the British fades as unscrupulous politicians in London and *Ottawa sell Mexico down the river by tacitly supporting US wars of conquest against Mexico, as an attempt to swing US opinion towards the Empire into a positive light. It works, and the public in the US by and large "forgive and forget" the former hostilities towards Britannia.

Just a few (likely plot holed) suggestions...