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.
To be honest, the easiest way of envisioning a border after is just to assume the 11 seceding states, and if you feel like being generous, the Indian Territory since it was split down the middle for much of the war.
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.
IMO plausibly the only thing that brings peace is going to be (regardless of the scenario) an election of a Democrat in 1864. This is something that I believe way too many people forget. If a Democrat (likely McClellan) is elected on a platform of peace or negotiations, the US will have willingly elected a government which was aiming to bring peace to the war. The Copperheads would, at least from 1865-1868 be seen as vindicated in their opposition to the war. Even in a Trent War scenario they will blame the entrance of the British into the war on Seward and Lincoln for allowing it to happen.'
Sure, by the election of 1868 or later there may be some 'buyer's remorse' when it comes to a treaty, but by and large the nation will have walked into it eyes wide open.
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.
Abolitionism and abolition as a whole, will depend to a large degree on when peace comes. Assuming, for the sake of it, a peace in 1864, then we have two important questions:
1) What is the status of the 13th amendment in the US? Did Lincoln manage to pass it, or is slavery still on the books in Missouri, Maryland, Delaware, and Kentucky? If so, that leaves about 300,000 slaves still toiling away in the Union (remember, the Emancipation Proclamation did not free the slaves in the Border States, or Tennessee). That will effect both the cause of abolition in the States and how it is seen abroad.
2) Did an electoral loss in 1864 come from a split in the Republican Party? OTL they almost split the vote, but Lincoln managed to keep the party unified. In a loss I can only see a split going worse as the Radicals pursue a more...well radical course and the moderates stick to their free soil guns and use the pre-existing issues of Western expansion and financial reform as their platform.
If any of those two conditions exist, then the cause of abolition will be a somewhat tangled one. Slavery still existing in the North would be a cause of ire to the abolitionists and they may feel compelled to 'clean house' at home before returning their ire to the CSA.
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!
Revolution of some sort is inevitable in the future of the CSA IMO.
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.
Relations with the British, assuming a Trent war, would of course be rather strained. Anglophobia (as you note) was still common in the US up till past WWII. On the flip side there would be lots of people in Britain with Yankeephobia(?) too who would have been glad to seeing the Union knocked down a peg. So grudges, ill considered diplomatic maneuvering and other problems would persist. However, I don't think either side would be looking to go for Round 2 any time in the 1860s or 1870s which may dampen the anger somewhat.
Even drawing on older models, the Revolution and 1812, then post war commerce and the 'common language' issue would probably pull the two nations back into cordial orbits. The trade was large on either side and there was too much money to be made. Diplomacy will continue apace, no matter what and both nations will be having dialogue of some sort.
Much does depend on the war though. Just assuming a Trent War, then you do have a situation where Britain felt compelled to enter the war when it did not want to. Their narrative will be 'the Yankees knew they were going to lose the war so they tried to compensate by invading Canada' while the American narrative will be 'Perfidious Albion was jealous and so entered the war to cut us in twain' or some such depending on the circumstances. Of course, it being a democracy the counter claim will be 'it was all Lincoln and the abolitionists fault' which will be rather compelling in some circles.
The treaty with the British too will matter somewhat. Quite frankly considering who was PM at the time I cannot see the British leaving the war without extracting their 'pound of flesh' from Washington, which will probably cause issues. Whether that is taking large reparations from Washington or something else, I don't know.
However, none of that equals a long standing alliance with the CSA. From all that I have read, at the highest levels of government, no one considered the CSA anything but a mere 'ally of convenience' if war came in 1862. They still viewed themselves as the Great Power and deigned to create lasting alliances until 1904 historically, and I can't see that changing here. The CSA, depending on its development, wouldn't necessarily rate Great Power status, and so would be problematic as an ally. Maybe a regional friend, or more likely a French stooge IMO.
But if its the case where alliance systems develop close to OTL (which I consider unlikely) then sure, an alliance with the CSA would make sense.
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.
It really depends. In the Indian Territory, they adopted some rather tame and generous treaties towards the tribes, even granting the possibility of statehood. Though I sincerely doubt the treaties would have been well honored (and Texas would probably have snipped the pan handle off) and the area opened up for settlement eventually. However, since many of the tribes did participate in the slave economy it would have been an interesting thing to witness.
That being said, the US might try more humane policies in this TL, but by and large the powerful plains tribes like the Sioux and the Comanche really didn't give a damn who led the governments in Washington (or in this case Richmond) and really just wanted to be left alone. They wanted their land to keep, and the US was incapable (or unwilling) to honor the commitments to the treaties they made with the Native peoples.
As a counterpoint, Canada led the somewhat "enlightened" method or organizing the treaty system using the numbered treaties. It still ended in the neglect and almost outright destruction of the Plains Tribes and a major uprising. I think that the two worlds were just too different from each other, and no one in Washington or Ottawa was really interested in understanding things from the tribes point of view. In a Confederate victory scenario, I still think the US would come down hard on the resisting tribes.