I don't believe I'm underestimating the US of TL-191. It's been a while since I've read the books, but I don't think I'm underestimating them. Yes, the US in TL-191 has a lot more experience with guerilla warfare (especially with the two Canadian uprisings and at least two Mormon risings) than OTL; but the military can only hold the territory if there is the political will to do it. The French in OTL more or less won the Algerian War militarily, but couldn't keep it because the French people had no interest in keeping politically.
It's one thing if Canadian or Mormon rebels/CIA target US military units. It's another thing entirely if they're targeting US civilians. It's the civilians who have the political will to keep up the occupation, and they're not used to being attacked for their government's policies. It's happened once, and that was the (failed) superbombing of Philadelphia by the CSA. They're not used to having CIA operatives target them, explode bombs in stadiums, car bombs, people bombs, shootings, because of US government policy.
And while the US armed forces are mighty (they fought a two front war on their own continent), they can't be everywhere at once. They don't have the manpower for it, there's only so many soldiers. They can't occupy everything. And unless they do scorched earth in Canada and raze everything Canadian to the ground, which would only drive more Canadians into the arms of the CIA and CNP, there are going to be gaps in their occupation.
My idea was to make Canada become like Northern Ireland in the Troubles or Algeria during the Algerian War. It's going to be bloody, and brutal, and the US is going to be maintaining two separate occupations of very hostile people, and that's going to drain on their economy (which would make their citizens very unhappy).
Ah you misunderstand, what i am trying to say that TL 191 is a much more bloodily world, than ours, a world where about seven nuclear weapons where dropped on heavily populated cities, where their is no Geneva convention or any sort of alternate to it, where tactics of mass shootings of civilians in retaliation of a resistance/ terrorist cell attack are common place, where imperialism is still alive and well, the new norm.
Yes i gathered that the CIA would and was targeting civilians but quite frankly that is even worse, yes political will is needed but again this is not the US of the OTL, this isn't the seventies US while in the middle of the Vietnam war where Americans where untouched by war at the home front, this is a heavily Militarized United States, conscription is mandatory, for the entire male population (the female population soon enough).
Where quite frankly as sad as it is the US national identity is heavily based on its history of war, to name a few, the war against England, for the Revolutionary War, the war of 1812, the quasi war, the indian wars, the war against mexico, then the war of succession, the second mexican war, then the great war and then the second great war, the basically was war every decade or two.
This is a US that had the entire state of Ohio virtually overran by the Confederates, and massive swaths of Pennsylvania destroyed, and areas of New England and Maryland bombed, and attacked at will by every instrument of war, a US cut in half, where yet another Mormon uprising happened, not to mention the Japanese and English Naval actions.
Side the military casualties, the death rates among the civilians would most likely be just as high due to the fighting(and the reprisals, mass targeting and other such acts), during the war to be heavily high, not to mention the Super bombing of Philadelphia, that type of trauma, the memories of that are going to last a long time, especially since a heavy population that survived the Second Great War are still going to be around ten to twenty years later.
So when a CIA or Confederate diehard bomb goes off in lets say independence square, or times square or in a heavy populated area in a major US city that kills about a dozen or so Americans, on American soil, in American streets, i would imagine that no their wouldn't be a weakening of will to continue to fight against such cells, dead bodies in such a scenario do not weaken will to continue to fight they strengthen it, ( the nazi bombings of london for example,) and this TL D.C and Philadelphia bombings, if anything Americans are going to be calling for revenge.
Which would inevitably lead to mass executions, which i do agree with you both that the US wouldn't just go scorched earth and level practically every city and town since it wouldn't just kill the Canadians who generally either support the US or are just keeping their heads down.
Instead i would imagine that just like every major resistance cell it draws its strength from certain areas in the country, certain cities, communities and residents, ( kinda like a South Korea, South Vietnam, via a North Korea and North Vietnam) inevitably political difficulties of this kind of magnitude would lead centralization.
Anyway such areas would be the target of US reprisals, leading to many other issues, more Canadians joining up, some refusing to join or even assist the CIA in anyway or form due to fear of the US.
And in such a scenario, the Army would by need have to remain large, to hold down both the former Confederacy and Canada.
And i have to disagree with you in economic matters, the US as seen by a earlier post in the filling the gaps thread would instal a resource control board to better mange the economy and it managed to due so for the entirety of the first great war and the second great war, so i do to see how a low level guerrilla warfare (i say low level since i do not think that the CIA or any Confederate diehard would or even could publicly rise in open rebellion without be almost instantly crushed) could cause enough economic damage.
Ok again sorry for the hurry writing and any spelling errors in advance i am still working, had to write this during my break, i had a lot i wanted to write on and a lot i wanted to explain more, but don't have the time,
Look forward to your response.