I appreciate that the foreign intervention theme has been deemed slightly off topic, but I really need to correct some misconceptions that seem to be present. Misconception one is what was actually being discussed in 1862:
In the fall of 1862, both Prime Minister Lord Palmerston and Foreign Secretary Earl Russell were ready to propose recognition of the Confederacy to the full Cabinet.
It's not recognition but mediation which was to be proposed (
“It seems to Russell and me that the Time is fast approaching where some joint offer of Mediation… might be made with some Prospect of Success,” Palmerston to Gladstone 24th September 1862). Recognition was suggested as the natural result of mediation being accepted by the South and rejected by the North, but the proposal to be made to Cabinet was not recognition as is commonly implied.
Only if the Confederacy appeared to be losing. If they appeared to be winning they probably accept the proposal and offer to fill the role as mediators alongside France (and potentially Russia as a counterweight).
It's not "potentially Russia"- Russia's involvement is seen as integral to the project. As Gladstone wrote:
"The interference which the case requires is an expression of opinion, or a course of action, on the part of such combination of the Powers as may virtually and constructively convey the prevailing judgement of the civilised world. The union of England and France would not sufficiently answer to this definition, for France, by her Mexican policy, has in some degree compromised her impartial, above all her unsuspected, position in American affairs. The union of England, France, and Russia would probably fulfil the definition... Russia supplies in the largest measure the one vital element, otherwise deficient, of traditional and unquestioned friendliness to America" (Gladstone memorandum, 25 October 1862)
Misconception two is that if it came up, it was going to happen.
If Palmerston, Russell, AND Gladstone had decided it was the thing to do, it's obviously going to be done.
This ignores the anti-intervention majority in cabinet, which I've highlighted on here before:
Those are the only three people who matter in terms of whether mediation makes it to cabinet, but they don't have the power to push it through. Let's look at the historical balance of opinion on mediation:
Supporters: Russell (Foreign secretary), Gladstone (Chancellor), Lord Westbury (Lord Chancellor).
Opponents: Sir George Cornewall Lewis (secretary of war), the Duke of Argyll (Lord Privy Seal), Sir George Grey (home secretary), Thomas Milner-Gibson (President of the Board of Trade), Charles Pelham Villiers (President of the Poor Law Board), the Duke of Newcastle (secretary for the colonies), Lord Grenville (leader of the House of Lords).
I don't see a victory at Antietam shifting opinion enough to overcome that balance. Most of those opposed stipulated that the North should show themselves to be tired of the war before mediation should be offered. If the only change is the Confederates winning at Antietam, that doesn't meet the criterion.
The only really powerful neutral is Palmerston, to be honest. The people I listed were the ones which historians have put on one side or the other: I would add Sir Charles Wood (secretary of state for India) to those opposed on the grounds that he later explicitly comes out and says they shouldn't offer mediation until it's asked for. That leaves the Duke of Somerset, Cardwell, and Lord Elgin, and- worthy though those gentlemen were- even if all three had supported mediation I don't see them swinging the balance.
The third misconception is the conflation of recognition and intervention. In fact, the main actors were careful to avoid such a conflation at the time:
"Many people who talk of acknowledgment seem to imply that that acknowledgment, if made, would establish some different relations between this country and the Southern States. But that is not the case. Acknowledgment would not establish a nation unless it were followed by some direct active interference. Neutrality, as was well observed by the right hon. Gentleman opposite, is perfectly compatible with acknowledgment. You may be neutral in a war between two countries whose independence you never called in question. Two long-established countries go to war; you acknowledge the independence of both, but you are not on that account bound to take part in the contest." (Viscount Palmerston, HC Deb 18 July 1862 vol 168 c571)
"The proposal would naturally be made to both North and South, if both accepted we should recommend an Armistice and Cessation of Blockades with a View to Negotiation on the Basis of Separation. If both declined we must of Course leave them to go on; If the South accepted and the North declined we should then I conceive acknowledge the Independence of the South, but we ought, Russell and I imagine, to declare the maintenance of our Neutrality even in the Case of our acknowledging the Independence of the South." (Palmerston to Gladstone, 24 September 1862).
"The choice, I presume, lies between inaction on the one hand, and an interference limited to moral means on the other... Recognition,... wisely accompanied with a declaration of continued neutrality" (Gladstone memorandum, 25 October 1862)
Naturally, this doesn't mean the US wouldn't declare war in the event of the UK, France and Russia recognising the Confederacy. However, I find it hard to see the US making such a quixotic gesture, and even harder to see any of the three powers entering into such a war with particular gusto- certainly not enough to prevent the US bringing its economic preponderance over the Confederacy to bear if they can find a few half-decent generals.
Indeed. I think it's hard for many modern readers to understand how the aristocrats back in the day thought about the issue, or at least in terms of nationalist pride and self-interest.
Perhaps it's difficult to understand because nationalist pride and self-interest almost never form part of these calculations? The discussion over mediation is generally what might be best for America, the slave and the world. In fact, the rationale for the timing of the intervention is to
avoid even the perception of self-interest:
"if in any one of the great towns... an outbreak should occur... we might then seem to be interfering... rather in the attitude of parties then as representing the general interests of humanity and peace" (Gladstone to Palmerston, 25 September 1862)
Given that I've got Gladstone out, I may as well end with a relevant quote:
Hell even OTL people were willing to overlook the slavery issue based on a set of prejudices and wildly inaccurate assumptions on the matter. The Confederacy enjoyed a baffling amount of support amongst influential portions of the population well into 1863.
"It is one thing to anticipate an issue of the war favourable in the main to the Southern view: it is quite another to sympathise with men whose cause is, as I think, seriously tainted by its connection with slavery" (Gladstone memorandum, 25 October 1862)