How Would An 1840s Anglo-American War Go?

[Hugh Third of Five]

The USN gets swept from the seas and America's overseas trade is shattered and choked off. Insurance rates rise in Britain from American privateers and raiders.

In the 1840s that wouldn't bite nearly as much as it did in the 1810s though. Sure it wouldn't be good for the economy, but the USA was in a much better position to get by with just domestic trade because the interior of the continent was much more settled. Also Britain would not be fighting Napoleon.

The 1840s saw a couple of problems arise between America and Britain- the Oregon Dispute, Paulet's expedition to Hawai'i, the Maine Dispute, and any other random problem on the border neither government might've cared enough to write down. So let's say that one of those disputes (probably Hawai'i, since it was a prime strategic area for either power,) blows up, and in 1843, the US declares war on the British Empire in order to 'liberate' the islands, no matter that London didn't authorize the invasion. How does the war go?

I think the Oregon dispute is more likely to get an American declaration of war.

 

[raharris1973]

I think the Oregon dispute is more likely to get an American declaration of war.

I think that's a dispute (as is the Maine dispute) where the Americans could have a more realistic theory of victory. For the Hawaiian issue, since the decider will be long-range naval power, I think America would contemplate war over that geography with feelings of inferiority.

 

[Naval Aviation Fan]

And army wise, would the US's invasion of Canada go any better than 1812? I can't really imagine it going too much worse since the front is a lot smaller without Tecumseh, but Canada (probably) wasn't run by idiots, and fortifications would have to at least be able to slow the states down, right?

In 1843, I'm not sure what the USA is going to be able to muster in a total war situation, but I suspect that the numbers are going to be far more than might be supposed here in this thread, as just 20 years later, the US was deep in the Civil War, and had ~1,000,000 men under arms, with upwards of 3,000,000 having served during the course of the war.

Best population figures I can come up with right now are:

Canada 1840
432,159

USA 1840
17,069,453

So, as always, the ground war potential is totally one-sided, and this means more than a 34:1 ratio in favor of the USA, so I cannot see any British/Canadian gains on the ground.

***Note, more recent and more accurate info has the above ratio shown to be very incorrect, and the best current info is more like 12:1 instead, just saying.

 

[AlexGarcia]

The 1840s saw a couple of problems arise between America and Britain- the Oregon Dispute, Paulet's expedition to Hawai'i, the Maine Dispute, and any other random problem on the border neither government might've cared enough to write down. So let's say that one of those disputes (probably Hawai'i, since it was a prime strategic area for either power,) blows up, and in 1843, the US declares war on the British Empire in order to 'liberate' the islands, no matter that London didn't authorize the invasion. How does the war go?

At this point, the US hasn't started the MexAm war yet, and it's not exactly renowned for its military power, but it does still massively outnumber Canada even this early on. but at the same time, this is like, the height of the Pax Britannica, the royal navy is untouchable, and London's not distracted by beating up a funny Italian man and his french empire anymore.

Despite where the war started, I suspect that the Caribbean will be the primary naval theater and that for a few years, the US economy is gonna be strangled by Britain. The question is- does the US have the means to build the navy to end it while at war? The country is certainly big enough to have those resources.

And army wise, would the US's invasion of Canada go any better than 1812? I can't really imagine it going too much worse since the front is a lot smaller without Tecumseh, but Canada (probably) wasn't run by idiots, and fortifications would have to at least be able to slow the states down, right?

In the event of an american victory, we know that the US would take the chance to get as much of Oregon, Maine, and Hawai'i (as a protectorate under the monarchy) as possible, but what about a British win? Would they push past the Columbia river in Oregon? What about hawai'i- they weren't happy about Paulet's attack on a sovereign monarchy they actually almost respected, but london would be stupid to give up that kind of position in the pacific

Independently of the outcome you are giving Mexico some extra time to prepare before the Americans decide to conquer the Northern Territories. That said, I don't believe the Americans will attack Britain until the war with Mexico (as in OTL) is over, to exploit their advantage over a dysfunctional Mexican government. An interesting possibility is that the war occurs during the Mexican-American War, essentially making the Americans having 2 fronts.

Aside from that, I suppose with the UK winning, Oregon will become inevitably another Dominion/Canadian territory. Even a status quo ante bellum would be de facto a British victory, since the Americans wouldn't get anything. And I don't believe another New Orleans situation will surge so another Era of Good Feelings rise.

In the case the US wins, the 54-40 claim will be enforced for sure, maybe even more.

 

[cerebropetrologist]

Best population figures I can come up with right now are:

Canada 1840
432,159

USA 1840
17,069,453

So, as always, the ground war potential is totally one-sided

Well, it will be, won't it? Sort of like calculating WWII as US + Russia + Britain vs Italy and concluding it'll be a walkover. Here's what you missed:

UK 1841
18,553,124

just 20 years later, the US was deep in the Civil War, and had ~1,000,000 men under arms,

And a population of 31,429,891, almost twice what they had in 1841, so you're looking at c.500,000. That's if they take this war as seriously as the Civil War, which I understand was a war to determine whether a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal can long endure, and as such you might expect both sides to put a bit of effort into it. For comparison, Britain in the Napoleonic Wars had a population of 12,600,000 (1811) and an army of c.250,000, so you're looking at c.375,000 on comparable population figures. Makes the calculus look a lot more even - certainly a more favourable ratio for the British than the War of 1812.

In the 1840s that wouldn't bite nearly as much as it did in the 1810s though. Sure it wouldn't be good for the economy, but the USA was in a much better position to get by with just domestic trade because the interior of the continent was much more settled.

Not what the US thought at the time we're talking about:

'a House of Representatives Committee on Naval Affairs referred to British commercial blockade as long after the Anglo-American war as 1842. At a time when a series of diplomatic incidents made another war with Britain a possibility, the Committee expressed concern over the defencelessness of the southern and Gulf of Mexico ports, vital not only for American international, but also internal trade. Their report, dated 12 May 1842 concluded, "If you desire to measure the hazard to which a maritime war with a formidable naval Power would expose this commerce, you have but to consult the testimony of experience."'

 

[Fabius Maximus]

That's if they take this war as seriously as the Civil War, which I understand was a war to determine whether a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal can long endure, and as such you might expect both sides to put a bit of effort into it.

Plus, in OTL's Civil War the Union needed to heavily import foreign arms and gunpowder for the first couple of years, because domestic manufacture just wasn't on a total war footing going into the conflict. ITTL this will obviously be much harder with the Royal Navy cruising the Atlantic.

 

[EnglishCanuck]

In 1843, I'm not sure what the USA is going to be able to muster in a total war situation, but I suspect that the numbers are going to be far more than might be supposed here in this thread, as just 20 years later, the US was deep in the Civil War, and had ~1,000,000 men under arms, with upwards of 3,000,000 having served during the course of the war.

That was in a near total war scenario, something even the War of 1812 didn't approach.

Best population figures I can come up with right now are:

Canada 1840
432,159

That's only Upper Canada (modern Ontario) from stats Canada we have incomplete numbers but Lower Canada (modern Quebec) roughly 600,000, Nova Scotia 200,000+, New Brunswick is 156,000. That doesn't include PEI and Newfoundland, but that's still 1.3 million.

So, as always, the ground war potential is totally one-sided, and this means more than a 34:1 ratio in favor of the USA, so I cannot see any British/Canadian gains on the ground.

It most manifestly is not and never has been. This is especially true in 1840, post 1838 where Loyalist militias had been armed and organized with 30,000 men under arms in Upper and Lower Canada. Comparable to what the US organized th invade Mexico nearly a decade later.

While the US could organize 100,000 men to invade Canada, it would take time but not be quick or easy.

 

[dfl_90]

I think the scale of this conflict has been aggrandized a lot. This is the period in which Anglo-American relations began to improve and the two achieved a number of notable compromises. Furthermore, economic ties were strengthening quite a bit as British investments poured into the US. The idea that two would fully mobilize and attempt to thrash the other into submission seems unlikely. I truly believe this would be a repeat of the War of 1812 in most regards. The British would probably make limited incursions supported by their naval supremacy and the American would likely defend themselves reasonably well on land while probing into Canada. Once both sides felt that they had reasonably defended their national honor, there'll be political and economic reasons for the two to sit down and negotiate an end to the war. That probably results in a resolution of the Maine and Oregon disputes, perhaps a bit differently than occurred in OTL depending on exactly how the war balances out.

 

[Kellan Sullivan]

 

[tallthinkev]

If it comes to it, there will be not much will be left of any US port on the east coast. Yes cities like New York do have some forts, but they will be not match for the RN, much more so as the US will be wiped off the face of the sea. The RN can mass their fleet/fleets and pick off each port one at a time. I won't be the burning of Washington of 1812, but the burning of Boston, New York, Washington, Baltimore, Philadelphia, Charlestown (plus the freeing of the slaves there).

The chance of freedom, may mean slaves revolts, troops will be needed in some places.
Giving money to Mexico regain Texas, or more

 

[Naval Aviation Fan]

That's only Upper Canada (modern Ontario) from stats Canada we have incomplete numbers but Lower Canada (modern Quebec) roughly 600,000, Nova Scotia 200,000+, New Brunswick is 156,000. That doesn't include PEI and Newfoundland, but that's still 1.3 million.

My thanks.

I knew something seemed off, as the ratio at different times was between 8-12 to one, but when I did that search yesterday I was to sick/tired to keep trying to get better info, and so just went with what I had. The 34:1 didn't seem to fit when at other times the ratio varied, but never came close to level. The 1.3 million figure, while perhaps not complete, gives us a much better comparison than those I posted in haste, without spending the effort to get better info. Thanks for the (better) info.

Well, it will be, won't it? Sort of like calculating WWII as US + Russia + Britain vs Italy and concluding it'll be a walkover. Here's what you missed:

UK 1841
18,553,124

I didn't miss this, I ignored it, and not because it is unimportant, mind you, but because I was (and am still) not feeling so good. That being said, it is good to have these numbers as well. Granted that a population on the other side of the Atlantic Ocean is not irrelevant, can we find a level of believability with a simple slider, based upon the times/means of shipping? For instance, it would be ridiculous to assume a 1:1 correspondence, even with today's technologies, as a population in the UK is not the same as them living in Canada, right?

So what kind of ratio equivalence would you propose with modern technologies, and how much less would that be, with more primitive shipping?

I wouldn't think the ratio would be as bad as 1:10, even in the days of wind driven wooden sailing ships/no refrigeration, but would also not buy it being as good as 1:2 either.

So, what ratio would need to be applied to a population's size to approximate it's ability to project power in the form of a ground army in North America, when the population is on the other side of the Atlantic ocean, as opposed to one the is already in North America?

And a population of 31,429,891, almost twice what they had in 1841, so you're looking at c.500,000.

Ok, I can see what your saying here.

That's if they take this war as seriously as the Civil War, which I understand was a war to determine whether a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal can long endure, and as such you might expect both sides to put a bit of effort into it. For comparison, Britain in the Napoleonic Wars had a population of 12,600,000 (1811) and an army of c.250,000, so you're looking at c.375,000 on comparable population figures. Makes the calculus look a lot more even - certainly a more favourable ratio for the British than the War of 1812.

In WWI, when France was invaded, they put more than 10% of their national population into the war. So we need to get that ratio and use that as a base, for a war in which British/Canadian boots are on US soil. A conservative look at the civil war numbers you have provided would give us what...?

Using the known to be less than France level of mobilization in WWI, of just 10% or 1:10 ratio of soldiers population, we come up with something like 3,000,000 plus troops, and checking with Wiki this is borne out pretty closely, right? Then jump back to the 1840 population, and apply the same ratio, and what do we then get...?

10% of the US population of 17 some odd million, would be a total of about ~1,700,000 troops total, with about 1/3 of that being peak strength, so something a bit north of the 500,000 troops in your post, so say 560,000 instead. But all of these troops are going to be drawing all their supplies/food from within their own country, not having to have them shipped across the Atlantic Ocean, on ships that have to rely on the winds blowing in the right direction. If the winds don't blow, or come from the wrong direction, crossing times are going to be longer than they were in WWI & WW2, and some of the foods are going to spoil even with perfect winds, so contrary winds will cause even greater losses in transit. Keeping in mind, every cargo ship that is repurposed from it's OTL activities is a disruption of British Empires commerce, which will be an additional loss over and above the direct costs of such a war.

Now in this hypothetical thought experiment, all the USA troops strength is going to be relevant to the ground war in NA, while only a portion of the British troop strength is going to be getting to NA, both do to shipping bottlenecks and commitments elsewhere, so my question would be, just what portion of that 375,000 figure is going to be in NA?

Keep in mind, the USA is a Nation, while the British are an Empire, with world wide commitments and obligations, so even if they wanted to, they cannot send everyone to fight in NA.

It most manifestly is not and never has been. This is especially true in 1840, post 1838 where Loyalist militias had been armed and organized with 30,000 men under arms in Upper and Lower Canada. Comparable to what the US organized th invade Mexico nearly a decade later.

While the US could organize 100,000 men to invade Canada, it would take time but not be quick or easy.

Never meant to imply that it would be quick, so sorry if that came across that way.

It certainly wouldn't be easy, either, and only British/Canadian boots on US ground, or raids on the US coastal cities, is going to PO the Americans enough to motivate them to carry this kind of military operation out.

I have a dim memory of the time I looked up a US v Canada war based upon then current populations, and discovered that the 5 US states of Ohio, Indiana, Illinois, Wisconsin and Michigan had a combined total of ~40 some odd million, while the whole of Canada had less than 30 million people. Keeping in mind, these 5 US states are not the most populated region in the USA, so New England, Florida, Texas, and California all have regions with even more people, so yeah.

 

[Vespasian]

The Royal Navy sails to the US east coast, defeats the US Navy in a series of battles, and proceeds to sail to New York, Boston, and Baltimore. Maybe New Orleans too...

The Royal Navy then smashes the aforementioned cities with cannon and shells.

 

[thesaturn]

this is the only bit i really disagree with, since AFAIK, Britain wasn't particularly expansionist in that region

while the states were pushing for BC and Vancouver island, I'm pretty sure the brits only really wanted what's now western Washington

yeah, pretty sure the british were content with dividing the area down the colombia river, so they could access it for fur trade

 

[Issei Uzumaki]

The Royal Navy sails to the US east coast, defeats the US Navy in a series of battles, and proceeds to sail to New York, Boston, and Baltimore. Maybe New Orleans too...

The Royal Navy then smashes the aforementioned cities with cannon and shells.

That conveniently leaves out the fact that after the war of 1812 the US invested heavily in coastal defenses. Having your capital burned tends to get people upset and want to prevent a repeat. So no, the RN is not going to simply show up and destroy every coastal city you listed.

 

[Tibi088]

In 1843, I'm not sure what the USA is going to be able to muster in a total war situation, but I suspect that the numbers are going to be far more than might be supposed here in this thread, as just 20 years later, the US was deep in the Civil War, and had ~1,000,000 men under arms, with upwards of 3,000,000 having served during the course of the war.

Best population figures I can come up with right now are:

Canada 1840
432,159

USA 1840
17,069,453

So, as always, the ground war potential is totally one-sided, and this means more than a 34:1 ratio in favor of the USA, so I cannot see any British/Canadian gains on the ground.

***Note, more recent and more accurate info has the above ratio shown to be very incorrect, and the best current info is more like 12:1 instead, just saying.

The problem with the idea is that it supposes this is going to be an all out war like the civil war was. I doubt that. This will be more akin to a colonial conflict. The british wont be looking to reconquering the US and the US will know this. I do not think that either side wants to go all out for the Oregon territoy and Hawai. I also doubt the conflict will last long - unless the US is way more successfull in Canada even initially than is expected because than it might turn into a major, all out conflict.

 

[cerebropetrologist]

For instance, it would be ridiculous to assume a 1:1 correspondence, even with today's technologies, as a population in the UK is not the same as them living in Canada, right?... all the USA troops strength is going to be relevant to the ground war in NA, while only a portion of the British troop strength is going to be getting to NA,

Indeed it would - as ridiculous to assume a 1:1 correspondence between the population living in the American South fighting on a front in Canada with 1840s railways with the population living in the American South fighting on a front in Virginia with 1860s railways. So you figure out how you weight your numbers to present the United States true strength, and we'll see how well those weighting assumptions might apply to the United Kingdom, in an era when even the United States finds it easier to send internal commerce by ship.

In WWI, when France was invaded, they put more than 10% of their national population into the war. So we need to get that ratio and use that as a base, for a war in which British/Canadian boots are on US soil.

No, we don't. French mobilisation in 1914 is determined by factors such as the mechanisation of agriculture and the dramatic uptick of crop yields, the profusion of railway travel that makes it possible to feed and equip those troops, the professionalisation of logistics and administration, the growth of industry to make them uniforms, and many other factors which are absolutely impossible for the United States of 1840 to match without a healthy dose of American exceptionalism. May as well give them tanks and have done with it. Even projecting the mobilisation figures of the American Civil War onto the earlier conflict is highly questionable, because the Union is able to mobilise all sorts of external resources which wouldn't be available to her if she went to war with the global hegemon which either produced the resources or can deny them to the US by blockade.

we come up with something like 3,000,000 plus troops, and checking with Wiki this is borne out pretty closely, right?

If you read the wiki and nothing but the wiki, sure. If you know that the numbers given in the wiki (2.2m for the Union, 1m for the Confederacy) represent not "Total number that served" but total number of enlistments, so that a ninety-day volunteer who reenlisted for three years and extended his service in 1864 would count as three people, or a 'galvanised Yankee' would count as one on each side, then the comparison starts to fall apart. But even if all you read is a wiki, it should be clear that France in 1914 is not the United States in 1840.

If the winds don't blow, or come from the wrong direction

A proposition somewhat inconsistent with the existence of trade winds.

all of these troops are going to be drawing all their supplies/food from within their own country

Are they? Can the United States, for instance, produce sufficient gunpowder to fight a war on the scale proposed?

every cargo ship that is repurposed from it's OTL activities is a disruption of British Empires commerce

Firstly, what happens if the British instead use their number of sail battleships in ordinary as transports en flute? Secondly, which is going to disrupt trade more - Britain taking up a small proportion of the largest merchant marine in the world to carry goods, or a British blockade shutting down the entire United States international and coasting trades?

Keep in mind, the USA is a Nation

The USA isn't even singular at this point in time.

while the British are an Empire, with world wide commitments and obligations, so even if they wanted to, they cannot send everyone to fight in NA.

Neither can the United States.

STATEMENT SUBMITTED BY THE CHAIRMAN OF THE COMMITTEE ON NAVAL AFFAIRS TO THE House of Representatives, in relation to the defenceless condition of the Southern coast of the United States and Gulf of Mexico. May 12, 1842...

my own attention has been urgently called, and I beg leave to invite yours, to the peculiar and most defenceless condition, not of that part alone of the Southern frontier of the United States, but of the entire coast and commerce of the Gulf of Mexico... since Florida has added to the maritime border of the United States more than one thousand miles, it has opened an inroad to the vitals of the South, of which an enemy would not fail to profit in any future conflict with the United States. Of the probability of an invasion in that quarter, in case of an unfavorable issue of the depending negotiations between the United States and Great Britain, the files of the English newspapers afford abundant and painful evidence. it is believed, if not known, that the tables of the British Premier would add largely to that testimony

New York, Boston, and Baltimore. Maybe New Orleans too...

That conveniently leaves out the fact that after the war of 1812 the US invested heavily in coastal defenses... So no, the RN is not going to simply show up and destroy every coastal city you listed.

Not heavily enough.

Report from the Chief Engineer... December 3, 1840

the work done upon the forts under construction has been directed, as far as possible, to bring portions of these successively into a serviceable condition. The result, however, from the entire inadequacy of the disposable funds, has fallen far short of what is demanded by the actual condition of the national defences. The appropriations of the last Congress, applicable to these objects, were not made till the middle of July; and, when made, the state of the Treasury attached restrictions, leaving the grants intangible for the rest of the year... The delays which seem unavoidably to attend the appropriation bills in their passage through Congress... have involved the loss of almost the whole of the working season of every second year

They touch explicitly on New York's vulnerability in 1836:

New York harbor... In the present condition of the defences of this harbor, an enemy would encounter no great opposition, whether his attack was made by land or water... coming into the lower harbor, he might, while the works on Staten Island are in their present condition, risk forcing the passage of the Narrows, as well as the upper works, anchoring in the Hudson or in the East river; or he might land in Gravesend bay, eight miles from the city, and march directly to Brooklyn, where he would find the navy yard lying at his mercy, and whence he might levy a contribution or destroy half the city. The only mode of resistance would be the expensive, harassing and uncertain one of arraying a large body of militia upon Harlem and Brooklyn Heights, and this could be resorted to only in the event, by no means certain, of receiving timely intelligence of his design.

Plus, in OTL's Civil War the Union needed to heavily import foreign arms and gunpowder for the first couple of years, because domestic manufacture just wasn't on a total war footing going into the conflict.

Not a problem so far: bear in mind that in 1861 the United States is caught on the back foot by the introduction of the rifled musket, whereas at this point the percussion musket is not dramatically better than the flintlock. The United States has a reasonable stock of weapons available for a 1840 war.

 

[Michael B]

Looking from point of view of Britain not supporting the CSA

1862
1) USA an important market for manufactured goods
2) Poor Russian harvests so need USA grain
3) Thirty years since the Slavery Abolition Act and twenty years suppression of the slave trade.

1842
1) USA a smaller market for manufacctured goods
2) Russian harvest no worse and probably better so less need for US grain
3) Ten years since the Slavery Abolition Act and maybe no multilateral treat of suppression of the slave trade.

Thus Britain may be more inclined to support any states that secede from the Union in spite of the slavery issue

From the point of view of any oligarchs running a cotton producing state they can either suffer a British blockade or they can secede and sell their cotton. Holding cotton back to drag Britian in a war supporting them is not on the table.

Also Texas not being in the Union shows that you can still be an American even if you are not in the Union. Thus there is a good case for some states concluding that secession is in their interests.

The USA isn't even singular at this point in time.

Less cohesion increases the possibility of secession. So peel off a sufficient number and the USA is facing a civil war. They won't be thinking about invading Canada or sending a garrison to Oregon.

Of course this CSA is as weak as a 1860s one so the British will have to sent troops to support them if secession is going to succeed. Success though means a client state beholden to Britain and politically a better output for a government than the stalemate of 1812.

 

[AltoRegnant]

Looking from point of view of Britain not supporting the CSA

1862
1) USA an important market for manufactured goods
2) Poor Russian harvests so need USA grain
3) Thirty years since the Slavery Abolition Act and twenty years suppression of the slave trade.

1842
1) USA a smaller market for manufacctured goods
2) Russian harvest no worse and probably better so less need for US grain
3) Ten years since the Slavery Abolition Act and maybe no multilateral treat of suppression of the slave trade.

Thus Britain may be more inclined to support any states that secede from the Union in spite of the slavery issue

From the point of view of any oligarchs running a cotton producing state they can either suffer a British blockade or they can secede and sell their cotton. Holding cotton back to drag Britian in a war supporting them is not on the table.

Also Texas not being in the Union shows that you can still be an American even if you are not in the Union. Thus there is a good case for some states concluding that secession is in their interests.

Less cohesion increases the possibility of secession. So peel off a sufficient number and the USA is facing a civil war. They won't be thinking about invading Canada or sending a garrison to Oregon.

Of course this CSA is as weak as a 1860s one so the British will have to sent troops to support them if secession is going to succeed. Success though means a client state beholden to Britain and politically a better output for a government than the stalemate of 1812.

Was secession on southerners minds at this point? I don't recall any threats in the 40s, unless I'm misremembering when the nullification crisis was

 

[Belisarius II]

Independently of the outcome you are giving Mexico some extra time to prepare before the Americans decide to conquer the Northern Territories. That said, I don't believe the Americans will attack Britain until the war with Mexico (as in OTL) is over, to exploit their advantage over a dysfunctional Mexican government. An interesting possibility is that the war occurs during the Mexican-American War, essentially making the Americans having 2 fronts.

Aside from that, I suppose with the UK winning, Oregon will become inevitably another Dominion/Canadian territory. Even a status quo ante bellum would be de facto a British victory, since the Americans wouldn't get anything. And I don't believe another New Orleans situation will surge so another Era of Good Feelings rise.

In the case the US wins, the 54-40 claim will be enforced for sure, maybe even more.

Mexico wasn't preparing for anything. The country was in a state of a long-term internal crisis that left it incapable of any kind of coherent national strategy. The British weren't going to occupy the Oregon Territory. The British population in the territory was made up of a few hundred trappers working for the Hudson Bay Company. Thousands of American settlers a year were starting to arrive via the Oregon Trail. The Americans had been purposing the 49th Parallel line for many years, and the British kept rejecting it. The 54/40 slogan was an extreme counter proposal to force the issue to a settlement, it was never what the U.S. Government really wanted. If there was a war in 1840 there was no way the British could impose any kind of control over the territory.

 

[Hugh Third of Five]

If it comes to it, there will be not much will be left of any US port on the east coast. Yes cities like New York do have some forts, but they will be not match for the RN, much more so as the US will be wiped off the face of the sea. The RN can mass their fleet/fleets and pick off each port one at a time. I won't be the burning of Washington of 1812, but the burning of Boston, New York, Washington, Baltimore, Philadelphia, Charlestown (plus the freeing of the slaves there).

Blockading a country is one thing. Raiding and demolishing port cities is another. Even if you have a powerful navy, your ships are still vulnerable to shore batteries. Sure Britain could capture or sack a city but not the entire east coast, not even close.

Giving money to Mexico regain Texas, or more

Firstly that assumes there would be a Mexican-American War in this scenario. Secondly if the Mexican war had already ended by the time this Anglo-American War breaks out, Mexico wouldn't be in a position to do much of anything. If this Anglo-American war coincides with the Mexican-American war, then I would give the edge to Brits/Mexicans, but an American victory would definitely still be plausible. If its after (or before) the Mexican-American war, or the Mexican-American war is averted, Mexico won't be doing much to help the Brits.

Looking from point of view of Britain not supporting the CSA

1862
1) USA an important market for manufactured goods
2) Poor Russian harvests so need USA grain
3) Thirty years since the Slavery Abolition Act and twenty years suppression of the slave trade.

1842
1) USA a smaller market for manufacctured goods
2) Russian harvest no worse and probably better so less need for US grain
3) Ten years since the Slavery Abolition Act and maybe no multilateral treat of suppression of the slave trade.

Thus Britain may be more inclined to support any states that secede from the Union in spite of the slavery issue

From the point of view of any oligarchs running a cotton producing state they can either suffer a British blockade or they can secede and sell their cotton. Holding cotton back to drag Britian in a war supporting them is not on the table.

Also Texas not being in the Union shows that you can still be an American even if you are not in the Union. Thus there is a good case for some states concluding that secession is in their interests.

Less cohesion increases the possibility of secession. So peel off a sufficient number and the USA is facing a civil war. They won't be thinking about invading Canada or sending a garrison to Oregon.

Of course this CSA is as weak as a 1860s one so the British will have to sent troops to support them if secession is going to succeed. Success though means a client state beholden to Britain and politically a better output for a government than the stalemate of 1812.

If you want a civil war over slavery and/or secession there has to be a reason for it to break out in the 1840s rather than the 1860s. A British blockade on cotton is would not do it even if there weren't a domestic market for it.

The problem with the idea is that it supposes this is going to be an all out war like the civil war was. I doubt that. This will be more akin to a colonial conflict. The british wont be looking to reconquering the US and the US will know this. I do not think that either side wants to go all out for the Oregon territoy and Hawai. I also doubt the conflict will last long - unless the US is way more successfull in Canada even initially than is expected because than it might turn into a major, all out conflict.

I doubt the USA will repeat the mistakes of the war of 1812, namely using untrained militias. I also doubt any attempt to conquer British colonies on the mainland of North America would be half-assed. If the USA chooses to fight, it will be committed to doing so. That doesn't necessarily mean going all in to try to take all of Canada, because it could mean pouring serious resources into Maine or Oregon. It also doesn't mean the attempt would be successful, just that a lack of American commitment to would probably mean no war to begin with.