I think the Union would look to changing the us constitution to ban any states succeeding from the union.
I think the enumerated powers would be expanded too to allow for more power to the federal government and less rights for the states.
Federal government might need to sell land to settlers to raise revenue. i could see new and higher taxes to pay for a large military and more powerful federal government.
I agree to all of this!
Of course here we have the stipulation that first the Civil War starts, more or less as OTL, then a Trent War situation develops and the Union comes to terms much earlier than its OTL victory, leaving the CSA unconquered. There is no development of the manner in which the Trent War happens, what each side accomplishes and loses, but if Britain is in a position to demand the USA recognize CSA independence, then clearly they aren't hurting too badly. I would think in these circumstances Canada is forfeit, at least temporarily, though it has long been my position in many scenarios that the USA, even if overall winning pretty well, would at least consider trading any Canadian conquests back for considerations elsewhere. This may come into play below. But the OP seems to assume the Union is in a pretty abject condition, and if we assume Upper Canada is in hand or anyway cut off from British help, say via a prior strike into Lower Canada severing all communications, then for the US to come to terms promising to leave CSA alone it has to be even worse off on other fronts. We just don't know the OP having left all that murky.
But the point is, with the USA capitulating, we don't know what condition it is in territorially. I don't think CSA is going to want anything north of the Border states, but perhaps counting Missouri as such--Missouri, if held in full, almost cuts the USA in half. Perhaps the upshot is a drastic rearrangement, with the USA laying claim to everything north of the Great Lakes and suffering some reversals in the Northwest (that region left to languish--it has some self defense ability but the British might be able to overwhelm it and take at the peace table all of OTL Washington for instance, so a highly unsettled situation exists of overlapping claims, the USA securing the Great Lakes region and thus claiming the plains west into the Rockies all the way to the Arctic Ocean, while the British holding an expanded BC claim the mountains and leave unclear just what their attitude is toward US holding Upper Canada; Quebec either spun off as an allied republic or incorporated as a state again with claims far north of its OTL then contemporary borders, the Maritimes remain British--all this versus the CSA demanding and getting all of Missouri but probably with few if any gains on the CSA's western bounds--I don't think the British will support these, certainly not if the USA does trade back at least some BNA holdings, and even distracted in a two front fight for her life and facing blockade, can spare enough manpower dispatched westward to parry CSA moves into New Mexico Territory and pro-secession insurgencies in California, which can also, particularly with help from Deseret, assist Union forces and NMT militia recruits on the Texas fronts. Post war I assume the US still has its western holdings north of Arkansas and Texas, pretty much perhaps with some border rearrangement; CSA does not have Pacific access and never will. East of Missouri, perhaps CSA with British reinforcement can drive Union forces out of Tennessee and Kentucky--bearing in mind they have to repress the mountaineer settlers who have zero interest in slavery. British aid would be most useful and forthcoming (aside from bogging down US forces in the Maritimes/New England front) on the Chesapeake, so I defy conventional wisdom and figure Maryland is forfeit to CSA as well--which means of course Washington DC is no longer a viable capital for the USA (it might be for CSA, but i suspect Richmond is as far north as they will want it and might be set up farther south--in NC, SC, Georgia or all the way back to Montgomery AL) and is ceded and presumably reincorporated into CSA MD; I have been put on notice Delaware was not much of a slave state, but even so I think in the context of a British championed CSA war victory the Confederacy gets it.
So the borders are much as I envisioned in other threads with the assumption there is no war at all, except the status of Upper and Lower Canada is very unclear, as is that of the territory that OTL became Washington State--I do not believe the British could spare the Pacific forces necessary to invest all of California, even if they hold key parts of it the state goes back to USA at the peace table and much the same for Oregon.
The exact borders in a Trent War situation, and salient to this thread too the nature of US political leadership, are very much up in the air. I can't visualize Lincoln capitulating as early as OP assumes so presumably he is out--and I think Hannibal Hamlin would fight doggedly too and manage, with the help of Lincoln's surviving circle, to keep the Union in the war longer. So, the leadership is very different than OTL one way or another. Similarly borders are very fluid. I presume the British would seek to reinforce Virginia in the lower Chesapeake and with naval force assisting push hard against DC, making it too hot to hold. OTOH, the Union has the opportunity to raise subversion in western Virginia, and the east of Tennessee and the mountains generally; at the peace table the CSA might have to agree to lose a deep salient just as the Union might need to surrender Missouri--or maybe not, it depends on how secessionist Missourians would be. Canada as noted is a huge question mark; a successful Britain might be able to insist on getting all of it back but perhaps only in return for giving back any territories in the Pacific Northwest and/or New England they might have seized. Note that in other threads where I assume no war at all, of course the US/British NA border is sacred, while I dismiss the possibility that the US could get West Virginia in any form--it is legally impossible for the US to talk peace with the CSA while openly aiding subversion against one of her key states! War opens up everything; a sanguine champion of the CSA/British alliance might have the Union cut in two and forced to submit to what amounts to British rule. (I think Britain's ability to sustain a long hard costly American war is undermined by domestic opposition; with no war this factor can be disregarded completely, with a hard nasty war it might lead to domestic revolution and the end of the UK).
This is my best guess at visualizing what a war as OP mentions would result in.
I think there would need to be a demilitarized zone at least around Washington D.C. and a shipping route for the union down the Mississippi.
Obviously if the CSA is able to seize or be granted Maryland, then Washington as noted is a dead duck and the USA has no access to the Chesapeake whatsoever, it becomes a CSA lake.
Similarly with the Mississippi--just as I claim that for the CSA getting Pacific access, "want" and "have" are quite different, so for the Union wherever the CSA is on both sides of the Mississippi, that's Confederate. Sure, historically there were different arrangements but those were hashed out when the Mississippi valley was mostly Native American inhabited; by the 1860s it clearly is a river under the control of whoever lives alongside it. Any Union trade to the Gulf is a matter of whatever the CSA wants to allow. I believe this would be true even in a "go in peace" scenario, and clearly must be if the British are in a position to demand the USA to capitulate. Maybe some later crisis or opportunity will allow the USA to gain this boon, but note that even if granted on paper as a practical matter the Confederates can nullify it any time anyway.
So here I disagree very strongly and in any CSA ATL, unless one wants to stipulate one where Arkansas and Louisiana somehow stay in the Union, which makes no sense at all. Maybe Arkansas, but Louisiana is clearly destined to be a charter member Confederate state. With the British backing them, forget it!
To be sure the value of the lower river as a transport artery is enhanced by US trade goods; it is not in the interest of either power to close the border to trade, unless one or both is bound and determined to fight again real soon.
I could see a lot of copperhead being persuaded to leave the union.
I don't follow that very well; at best you'd have to unpack it a bit. There were many different forms of opposition to Lincoln's policy after all. Some "copperheads" would be Northern Democrats who feel that the Union is better off forgetting all about slavery or the consequences of trying to abolish it; others are people with a mix of sympathies for the South or particular Southerners and/or economic interests in them. Certainly one consequence of Britain joining the CSA side is to make the whole mess of the war more unambiguously a matter of USA patriotism and anyone who opposed the Union regime is under some suspicion beyond OTL--but on the other hand the other side clearly won. I think while there will be some cloud over the anti-Unionist political position in the North, on the whole it will survive as legitimate opposition. Indeed particular individuals who committed open and shut instances of treason might be exiled--or more likely, if caught, executed. By due process of law, and anyone who was not caught and tried and punished during the war seems likely to get off after it. Perhaps being so unpopular they decide to leave on their own--"persuaded" as you say, but this is a matter of exemplary punishment and/or shunning and persecution of egregious examples, not a wholesale purge I think. Some people will be less rather than more comfortable as time passes and consequences unfold, and these will leave...but meanwhile others in the South will up stakes and move north too; they might be met at the border with some suspicion but I believe not a few will have or claim pro-Unionist credentials and these will be welcomed in.
The underground railway will still help escaping slaves, not sure who welcome they will be in the Union so they may need to continue their journey to Canada.
I think so, and also share your ambiguity. The abolitionists will be fewer, most of their penumbra of fair weather friends at first drifting off thinking "well, now that's settled we don't need to worry about those poor black folks, our hands are washed of it." However factions who wave the bloody shirt of British perfidy and Southern treason will at least tactically want to claim the mantle of some kind of abolitionism.
Before the secession, abolitionists were a domestic subversive movement in some views, causing needless unrest. Some people will now blame them for the manifest harm to the union they will hold could have been prevented if they had just minded their own business, and the hostility might be quite violent. Now they are subversive in the sense of tending to promote war with a dangerous foreign nation probably entangled with other dangerous foes. But to some Americans picking those very fights will become a proposed identity for the USA.
As a practical matter, slaves will continue to flee the South. It has been suggested on other threads that the CSA will hardly sustain slavery forever. But if the solutions of gradual emancipation fashionable to people who find the horror of ongoing slavery unthinkable and therefore of course necessarily irrational and unlikely one way or the other were terribly practical probably slavery would not have been such an unsolvable dilemma for the USA OTL! In any case, whether chattel slavery in the familiar form can be modernized and continued, or some mutated collective form develops, or in fact the slaves are emancipated gradually, I expect Southern society will depend on them and their descendants being kept in some subordinate position, there to take falls and blows and suffer shortfalls and do hard work so white people can minimize their having to suffer any of these things, and however the problem of forcing this service out of them is solved, there will be terror and gross plain injustice. Since these things have remained true to some extent here in the USA OTL I am pretty confident they will be in the ATL too, but an international border now separates most AA exploitation from direct observation and formally speaking absolves the Northern people of responsibility--or authority to do anything--just as this distance exists between the CSA and Britain.
But whether legally slave, government owned forced laborer, lower caste free person with rights such as they are recognized at all subordinated to any white person who moves among them, or whatever, these people will be resisting this programmed fate in various ways, and will try to get out as one of these paths. Conceivably some economic, political and social juncture might arise where the South's rulers decide the day of forced AA labor has passed and now suddenly they want to be rid of them, and open the gates and let them exit wherever they like, but I doubt it will ever work like that.
Slaves, or whatever insulting and painful status they are accorded as the CSA progresses, will probably be trying to escape against the will of the white ruled society, and a certain number will manage to accomplish the trick. Landward the only available borders are into Mexico, and into the USA. Both countries will be under some pressure to return these fugitives to their custody, but now no one outside the CSA has any actual legal mandate to do so; it is a question of diplomatic expedience and nothing more. That being so the question remains one of vexing political importance.
Note that from the CSA's point of view it matters little whether a fugitive is allowed to settle on US soil or if they are gathered up as fast as they arrive and shown to other borders, placed on ships bound for Liberia or straight to Great Britain--the CSA interest is that the fugitives are returned specifically to them, and any nation that does something else is denying the Confederates what the founding generation at least calls their property. I might suggest then that in conjunction with the abolitionist voice of conscience whispering in the larger public's ear, insofar as the USA does anything other than remand them back to CSA custody, they settle on instead letting the fugitives take up residence in the USA and become citizens. That way, while not annoying the Confederates any more than if they did something else to pass the hot potato along, the USA gains the benefit of immigrants already proficient in a version of English, probably in some way or another competent to do useful work of a modern kind. And in addition to that, if their welcome in the Union is warm enough, citizens who have a strong motive to oppose in particular CSA expansion or invasions of the USA! (Also if the British alliance continues to be a thing benefitting CSA, these African Americans will probably have some reliable animus against the British Empire as well). So overall either the US policy will be to remand them back to CSA custody, or increasingly to let them settle in the USA--especially remembering that Britain is stipulated to have sided with the CSA and thus passing fugitives on to Canada, or their trusting their chances on the high seas in transit to anywhere, or that CSA raider ships might not descend on them to recapture them on whatever shores they might find some apparent safety, are all in some awkward doubt due to Britain's complicity. Of course the CSA is in no position to demand anything of the British or any British subjects anything no strong interest in Britain will agree to; the purported Trent War alliance might be very temporary--but that does leave the CSA alone with the USA.
In this context I think abolitionism as such remains salient and survives; amid much controversy. US policy may vacillate between appeasing CSA demands for repatriation and refusal to do so; in the conciliatory periods abolitionists will be out of style and perhaps criminalized; certainly some hard core abolitionists will break the law and in a systematic, planned manner, whenever the law insists they must turn over a fugitive who reached their arms and was given their protection and help.
I could see abolitionists turning to other moral causes like banning alcohol, and maybe drugs and other vices.
Certainly such crusades will be undertaken and there is a natural linkage of all to each; the Prohibition party was a perennial third party for a very long time in US politics. Feminism is historically intertwined with abolitionism in US history as well. The anti-drug stuff, focused on booze, is likely, but it will not be a matter of people who just want to make trouble and preach having to find a new hobby! There remains plenty of abolition work to be done in this ATL and there is no reason to get off that hobbyhorse if one conceives of these movements as that. Each strand of radical reformism will be itself, its own identity and movement, but much intertwined with the others to be sure.
Don't forget the radical labor movement! In an ATL with the USA and CSA separated abolitionism will remain part of the package of left wing standard causes.
There could be a lot of people turning to religion to explain the defeat.
I think that would be very odd. It's not like a meteor wiped out the Midwest. The slavocrats committed gross treason then the corrupt rulers of the British Empire, the Enemy of Mankind in the Irish phrase, teamed up with them to sucker punch the Union. The mysterious will of God is hardly needed to make sense of things here; rather the presumption would tend to be that this is a case of the Devil having dominion over the world and the Union, particularly if it avoids too much dishonorable compromise, can be glibly assumed to be on God's side. The passionately religious we will always have and their roles in the USA can be strong...but I see no reason for this entirely manmade catastrophe to disrupt the general alternation between secularism and Great Awakenings that cyclicly rock the American mind.
It might do something to sustain rather than inspire the kind of religiosity such abolitionists as Harriet Beecher Stowe expressed, but most likely her to the modern reader remarkable steeping in Christianity as lens is simply a matter of her place and time. Indeed passion as strong as religion might be needed to stand fast as an abolitionist, particularly one who proposes to venture into the heart of darkness and invade the CSA (as stealthy agents I mean here, not en masse) to steal more human "property" than is capable of liberating itself successfully; the penalty for losing points in that game is death after all. Probably with some kind of torture first.
But this leads me to again wonder about the trajectory of radical labor in general. The thread focuses on politics in the Union but we have to wonder what is going on south of the Mason-Dixon line too. It is my belief that if the secessionist fire eaters are rewarded with success in their rash enterprise, they will ride high in the South and double down, distorting all decisions to favor their peculiar position. One possible outcome of this is a failure of liberal cooption of the large part of the working class--it goes without saying that about a third or more of that class is in fact African American and in lieu of the usual divide and rule on subtle lines of class status, with the most potentially effective potential working class leaders being lured into "middle class" respectability, the gross division of humanity will serve instead, with lower echelon type "whites" both bribed by the flatteries and privileges of white supremacy and as terrified of the perhaps inevitable day of judgement when the slaves get loose at last--as their archetype Jefferson said, "I tremble for my country when I reflect God is just." This form of white guilt might serve to enable all sorts of barbaric solutions to the basic problem of how to get useful labor out of a group with practically zero hopes and nothing to lose.
I think it is possible though that in their arrogance and losing the habit of effective conciliation of working class interests, a lot of white people might themselves suffer serious alienation, and to at least some of them, the racist scales over their eyes blinding them to the shared humanity of the bound class might erode away and the prospect of an interracial radical alliance open anew. This alliance has no pretense of being gentle, gradual, or legal; having "no rights a white man is bound to respect" any whites linking their cause to the slaves are declaring war on all of Southern society, much as Huck Finn reasons out that if he will not turn Jim over to the authorities as a fugitive slave he must be damned to hell, and he resolves to make the most of it.
The possibility of Red Revolution in the most luridly violent and stark form overtaking the CSA seems like it might be a real one to me!
A union with hostile relations with the British empire the Union might be a place where those who rebel against the empire will see support,eg the Irish, the Boers, Indians etc.
To an extent this was true OTL as things were; Anglophobia did not become a rare thing until the USA plainly surpassed the British Empire in the cours of WWII and many a decision or attitude during that war is blamed on lingering Anglophobia, despite the clear tendency of the USA and Britain to converge and support one another from the end of the Civil War era on. Like so many things we are discussing here it does not do to pretend the USA, or Britain, or CSA, is just one person with one settled policy in mind; each nation is layered with many classes and with people on more or less the same "level" of society often living very diversely from each other and with even individuals in much the same position both vertically and horizontally still splitting into opposite camps. The American view of what Britain is and stands for takes another heavy blow here to be sure.
A lot depends on how the British behave down the line. Backing the CSA diplomatically was bad enough for the British left OTL; getting in and out of a Trent War quickly and with some glorious victories to point to (whether or not there are also ignominious defeats!) will tend in the short run to bolster the right in Britain, much as Thatcher's conduct of the Falklands war was quite effective in quelling leftist credibility in her day. Glory, honor for the fallen, and success will cover the sordid fact that the great champion of emancipation Britannia has chosen to rule the waves on behalf of the slavers of the South, for ongoing profit of the textile mills and to undermine the beacon of republican liberty across the Atlantic many a Briton hoped perhaps to emigrate to--to an extent. Unlike my own preferred scenario for CSA probable survival in which the Union leadership waffles and temporizes and decides to let them go with no war, however, here the Union did throw down the gauntlet to the secessionists and fight--only to be ganged up on and beaten. To be sure if the Union strategies and policies parallel those of OTL closely, the narrative that the Yankees care no more for the slaves than their southern cousins do will have more credibility, but I suspect if the Union is confronted with an Anglo-Confederate alliance desperate expedience will light a fire under the commanders and they will in fact act to mobilize slaves against their masters; some form of Emancipation Proclamation, perhaps less underwhelming in its wording or boldness of application, will quite possibly emerge much earlier, and troops of color will probably be wearing the Union uniform before the leadership calls it quits. So on the left, if any of this happens and possibly if it does not, America--meaning the USA--will take on a brighter coloring and the perfidy of the ruling classes be the more tainted with guilt.
Will Britain persist in the OTL liberal course, or be turned to a starker class struggle? Meanwhile will British foreign policy cling to the CSA alliance, or drop it after the peace of 1862 or '63? If the regime, suitably purged by falling governments, repudiates the close alliance with the Confederacy, it is possible that the bad blood dividing USA and UK will be diluted over time and the positive attractions of two English speaking liberal regimes both in the forefront of world capitalism will draw at least their dominant elites together much as OTL, leaving the waving of bloody shirts for a bunch of dissidents out of power. All this bodes ill for the CSA of course, especially as it can't be more than a few decades at most before "King Cotton" is well dethroned, by alternative sources, by soil exhaustion, by such disasters as the boll weevil plague, and if the CSA has not diversified its portfolio considerably in the profitable years--and the feckless nature of secessionist leadership especially in matters of pragmatic business suggests to me it would be optimistic for anyone to hope they will--the rug will be pulled out from under rather brutally.
Longer term I cannot see the union getting involved in wwi other that selling materials for cash.
That would depend on how both CSA and British holdings north of the USA develop. If the two former US federal republics are tense, on a plain collision course, each building up force levels to credibly threaten the others...the standard trope of each joining one side with the other the other of a world (well, North Atlantic centered world) system building to world war seems likely indeed. As noted by others, the purpose of an alliance is to tie down one's likely foe or their best allies on another front, rather than as some seem to think coming to the direct aid of the other.
But supposing the CSA develops as a pariah nation, a stagnant hellhole of backwardness and barbaric institutions, with all manner of fire eating rhetoric but little credible force to back it up. The USA must I think be more military, maintain a higher level than was the case OTL. Isolationism as OTL might be an option, mainly if the USA is in fact aligned to Britain. I think the USA in the immediate wake of the humiliations of 1862 would among other things cultivate an alliance with Mexico and cultivate her development--so nothing analogous to the Zimmermann note (or the incursions of Pancho Villa on the southwest border to give the former more credibility) would be likely to happen, but perhaps as OTL similar factors draw the reduced USA in to weigh in decisively on cinching victory for whatever side they join; if the CSA seems manageable they will be left to stew--joining the other side as an ally might be a death sentence for the regime and the OP wants to see it survive, so presumably they have enough brains to stay put, either support the winning side themselves or just sit tight as irrelevant neutrals similar to the status of Latin American nations, even the largest, OTL.
Again declaring one possibility as definite and the others mathematically excluded seems going way beyond what we can decree without gaming out a picked scenario in detail.
American Indians still do badly or worse.
Elsewhere I have been contrarian about the standard CW trope that the Native peoples were somehow in the CSA's pocket. Some might have been but other tribes I think were not. Whereas if a split between North and South becomes permanent, the Indians are in a negotiating position, and the Union has more to offer I think--vast northern and western territories as yet unsettled by Anglos for instance. Also I think a counter narrative to the OTL predominant European supremacism has more scope in the North than in the South. I think it is at least possible Native peoples, or anyway various tribes that lay their bet down on supporting the Union, can do a lot better than OTL.