A few more comments, having read some of the recent posts.
Firstly, HT is writing the book, so what he says goes, in which case a rerun of the Eastern Front of WW2 is most likely.
It is true that we don't have any details as to force compositions, numbers and so forth. Nor do we know much about relative industrial capacity. in this case, much of what I have to say is by inference.
Oil - I am aware that Texas-Oklahoma was not the only source of oil in the USA;just that by comparison these were by far the largest. Oilfields in Pennsylvania and Indiana are likely to be vulnerable to CSA forces. I think the main exploitation of the Canadian fields came post 1945 in OTL. Assuming earlier development, they could be vulnerable to Canadian sabotage.
I still think a lack of oil could be a problem for the US. I am also assuming that CSA offensives into Sequoyah and from Texas would serve to place their oilfileds out of US range.
Society splits. The US is not a united nation - there is a strong divide between Socialists and Democrats (or Labour and Capital). There also appears to be a strongly pacifist element in the US. Flora Blackford (Hamburger) exemplifies this, although oddly she is one of the more anti-CSA characters. It is rather akin to European pacifist parties in the 1930s- war was so terrible that its use should never be considered again. Laudable but it does pressupose goodwill on all parts. However, I do take the point that an unprovoked CSA attack may override this and bring the parties together.
So far the CSA goes, Featherstone has pretty well united the white and hispanic population behind him - opposition from that quarter seems to be muted and limited to old style southern aristocracy. I expect this to be as futile as similar oppostion to Hitler. There is, of course, the persecution of the coloured population. I doubt that this will seriously degrade the CSA's ability. Both the Nazis and USSR managed to exercise power no matter how bad the situation. Also the CSA has the reality of the revolution in 1915-16, the CSA version of the 'stab in the back' and Featherstone won't let this happen again. Where it may backfire is in the attitude of his major allies, France and the UK have large colonial empires and also large numbers of colonial troops. Mind you, the US/UK stayed allied to the USSR in WW2 and Stalin was equally as brutal.
There are some other thoughts that I have had or that reading other posts have raised.
Japan. This is an enigma. All that we know is:
it has fought an inconclusive war with the US
it is involved in China probably more successfully than in OTL
it has control of the Philipines (since before WW1)
it has effective control over the Dutch East Indies and French Indo-China
This gives it extensive control over commodities such as oil and rubber but probably not enough for export purposes. I suspect it would be happiest staying out, contenting itself with any easy pickings. Unlike OTL, it hasn't had to contend with a US-UK inspired naval treaty which appeared to hamstring it (and other minor naval powers), nor with any western opposition to its role in China. I see no reason why it should involve itself in an American & European struggle now. Much better to let the foreign devils gut themselves. There may be, from the UK point of a view, a negative effect in keeping Indian and Australasian forces where they are.
Europe - happily involved in its own little maelstrom will play little part in this war. The exception being the navies, the RN in particular. I would imagine, as with the Axis powers in OTL, some surreptitious and then flagrant breaking of the peace treaties would occur. As to the fleets, I suspect more of a cruiser-carrier fleet - again an assumption, that the defeated parties learn more than the victors and have to work around treaty limitations.
UK assistance to a Canadian revolt may also occur but this will be difficult to arrange to anywhere other than the Atlantic provinces.
Other than that, we know little about events in Europe. I'm guessing the Germans will lose.
Industrial capacity.
We have become so used to the US being an industrial superpower that there is a tendency to assume the same in the books. I suspect the gap between CSA and USA may be less at this point. OTL comparisons are not strictly valid.
Firstly, a lot of OTL industrial capacity was funded in the late 1800's from the UK. In this timeline, I suspect that most of that investment went to the CSA and S America. This would not prevent the USA developing its industry but may have slowed it. Maybe it would have had no real effect.
More to the point of thie next books, US industry was badly hit by the depression. Even as late as the late 1930's people were losing their jobs due to the slump. In OTL, New Deal and, more importantly, rearmanent first in Europe then in the US itself was a major cause in an industrial pickup. In this timeline, any Franco-British rearmanent is going to stay homegrown or be sent to allies. Similarly, the rush of orders that occured in OTL 1939 isn't going to happen, Again, conjecture, but I don't think President Smith psuhed through an increase in defence spending in his first term. His predecessors were even less disposed to spend any goverment money (or taxpayers money if you prefer). Incidentally, I liked the point raised about whether or not the Hoover Dam project went ahead.
Conversely, Featherstone did institute a major industrialisation progamme in the CSA; a CSA that probably had a larger industrial base than that of OTL. Whether this would be sustainable in a wartime economy is another matter.
Regarding industrial capacity - a lot of US industry is within striking distance of the US/CSA border - as I said the straight line distance from Louisville to Chicago is about 250 miles. If a wide envelopment is planned, then the distance is much longer but still achievable. Virginia to Pennsylvania is a bit less but less vulnerable as the border is more heavily fortified - this, I presume is where the US expects the CSA to attack as that was the main CSA attack in 1914.
The option used by OTL USSR was relocation to a secure area. I cannot see this being done by the US; partly because Stalin was able to enforce compulsory movement, an option not open to the US, partly because the relocation in the USSR was a fall back trading space for time. The US hasn't that much North-South space. Lateral routes East-West are vulnerable to the CSA, the Mormons and to Canadian insurrection.
An area not yet touched upon is military leadership. Morrell appears to be a competent officer with a grasp of modern warfare. His low rank within the US hierarchy shows how much of a necessity that is for the US army. He would appear to be a De Gaulle type figure. Dowling, the aide to Custer in WW1, resembles Gamelin (aide to Joffre) or Weygand (aide to Foch), an able administrator and strategist but probably not capable of reacting to a fast moving situation. I suspect his fellow army commanders to be similar - Certainly, US leadership in WW1 was hardly inspired and it seems to be that generation in charge, especially as most real talent would more than likely gone into business post war.
Finally the A-Bomb
The physics side was probably on a par with OTL. However, I doubt any one of the powers is in a position to make one in this timeline. It was a major scientific and engineering undertaking involving resources from more than one country - Where in OTL all this expertise was concentrated in the USA, here it would be scattered. I think we can leave nuclear flame over Richmond to the next war in the series
