If you are talking Confederate offensives in general, you are also wrong. The Union was able to concentrate forces at Antietam and Gettysburg, but even when they couldn't, the Union beat the Confederacy. At
Chickamauga, the Confederates outnumbered the Union. While the Confederates won that battle, General Bragg frittered away the results of that victory until the Union could concentrate at Nashville and a month later the Confederates were retreating, which does make it the second most effective Confederate offensive into Union held territory. Even when the Confederates concentrated forces against the Union, they were typically unable to defeat the isolated Union forces before the Union could counter with a concentration of their own. Due to Wallace taking the wrong road, the Confederates had a numbers advantage for most of the day at Shiloh. Hood outnumbered Schofield better than 3-to-2 at
Spring Hill, but failed to crush him. At
Franklin, the Hood's Confederates outnumbered the Union, but took 3 times the casualties and again failed at preventing Schofield from linking up with Thomas. Then there are times when the Union had no nearby forces to concentrate with and the Confederate offensives still failed. At the
Second Battle of Corinth, Van Dorn's Confederates had almost the same number as Rosecrans Union forces, but the Confederates lost. At
Fort Davison and
at Fort Sanders the Confederates (Price and Longstreet respectively) couldn't destroy Union forces (Ewing and Burnside respectively) that they outnumbered by 6-to-1 and in both cases took about six times as many casualties as the Union. At
Helena, the Confederates under Holmes had almost twice as many men as the Union forces under Prentiss,, but the Confederates took about eight times the casualties. At
Pea Ridge the Confederates under Van Dorn outnumbered the Union under Curtis by 3-to-2, and the Confederates lost. Confederate troops under Hindman outnumbered the Union troops under Blunt at
Prairie Grove, but the Confederates lost. At Cheat Mountain, Robert E Lee's Confederate outnumbered Reynold's Union troops by better than 3-to-2, but the Confederates lost.
Let's look at the way you describe those examples:
Chickamauga - the Union
concentrates at Nashville (and the subsequent campaigns in Chattanooga have a greater Union force than a Confederate one). The Union draws in reinforcements from elsewhere to strengthen their position, and ends up with more troops because they have a deeper well.
Most of the rest are basically making the point about the power of the defensive on the battlefield, something I never really contested (in some cases it's about the power of the defensive for forts). The thing is, though, that the Confederates in a given theatre tended to have fewer troops overall (because they concentrated their forces in Virginia), and this meant that the Union could avoid leaving points vulnerable (by garrisoning them) instead of having to pull in garrisons to make a field army in the first place.
Offensive
campaigns are what should be looked at, not battlefields. For example, the Heartland Offensive manifestly suffered from a vast disparity of numbers (Bragg being outnumbered more than 3:1 at Perryville, which is generally viewed as a battle featuring the full campaign forces of both sides) and the place the Confederacy repeatedly got troops into the Union was the Eastern theatre, where the CSA prioritized it much more than the Union and so the force counts were relatively close to even (if not superior for the Confederacy at times, though not during actual offensives).
ED: some of those examples are poorly presented or in the wrong category - Cheat Mountain never really happened at all (the attack wasn't launched) and Prairie Grove saw the Confederates retreat in part because the Union
was bringing up reinforcements (so it shouldn't go in the "no concentration" category).
Your argument as presented earlier (Confederate offensives tended to fail) has five possible readings:
1) The Confederacy tended to fail because of structural problems relating to a lack of resources (men, guns, rifles).
2) The Confederacy tended to fail because the Confederate Army was incompetent.
3) The Confederacy tended to fail because Confederate generals were incompetent.
4) The Confederacy tended to fail because the areas over which they attacked were highly defensible.
5) The Confederacy tended to fail because all offensives are hard.
Now, of these I tend to view (1) exacerbating (5) as the most credible, because the Confederacy was (especially later in the war) on the wrong side of a resource disparity. The alternatives are essentially that it's ASB to expect there to be a competent Confederate general, which is risible on the face of it, or that it was a feature of where the fighting was taking place.
However, your argument as elaborated upon seems to suggest that you feel (1) was unimportant compared to the other points.
Even in a Trent War, the Union should be able to field almost twice as many forces as the combined British and Confederate forces in North America, which is better odds than the Union faced in most of the battles I have listed.
Really?
How?
We do have returns for the size of the Union Army in early-mid 1862, and we know how many small arms they had in store on 30 June 1862 (which included large numbers of imported British Enfield rifles, most of them arriving in 1862). The numbers simply do not add up.
If you feel they do, then please explain what number you feel that "almost twice as many forces" is - complete with some indicator of what you think the realistic British commitment would be, and preferably what you view the strength of the Confederacy as at the same time.
This is an extraordinary claim by you, and as such demands at least ordinary evidence.
Of course, if the Union
could field the number of troops you suggest, then they should have won the war rather easily in 1862 by launching attacks all across the Continent at over 2:1 odds everywhere.
Self-evidently, they did not.
In fact, this point of yours directly contradicts the argument you made above (which was that the Union did not rely on superior numbers) - both can be false (in the case where the Union had a slight advantage in early 1862 which expanded as the war went on), but both cannot be true unless the Union was OTL commanded by fools.
The idea of the Confederates getting in a quick strike before the Union can organize does not makes sense. The Union started the war with an army, the Confederates had to build theirs from scratch.
But the Union didn't make a call for more than a few tens of thousands of troops until July - and, more accurately, the Union started the war with about a division, which spent most of the war as formed troops instead of breaking up for cadre (probably because it had to absorb a lot of new recruits just to reach authorized strength).
The Confederacy would have to produce at least one general who equals or exceeds Lee just to gain independence. Keeping all of the 11 states that seceded is even more unlikely. The Confederacy gaining any bits of the Union Border states is nigh-ASB.
That's certainly your opinion, but it doesn't really address the point which I was making - which is that we're discussing the idea of a
successful Confederate secession. I can think of several possible avenues for that to happen (Fremont wins the Republican nomination and the Presidency, but goes full Emancipation once in office and every state with slavery secedes; rapid campaign against Washington in late 1861; Trent War; Peninsular Campaign goes horribly wrong and Army of the Potomac surrenders in early July...) but the point is that we should at least
look at how important the Border States were economically to make a proper evaluation of the economic issues.