Do you think the Swedes would necessarily win against the Commonwealth or did the Polish have a fighting chance? I mean several of the battles in the Polish-Swedish war ended in Polish victories..... I guess it depends on the Polish generalship. I wonder if we could see an attempted Polish conquest of Prussia? Though that would depend on Brandenburg getting involved in this TTL Northern war. I suppose that if the Hohenzollerns are blocked from the Pomeranian inheritance we could see them attempt to link Prussia and Brandenburg like they did later in OTL. Hm, could a Polish-Russian alliance against Sweden be in the cards? On the domestic front, would we see an earlier Reduction of fiefs or was that only necessary due to alienation of lands during the Thirty years' war.
From what I can tell, the best bet to make the Anglo-French war longer and better for England would be to eliminate the Duke of Buckingham early on (maybe die in battle or from illness) and replace him with a more skilled commander. Maybe the Earl of Essex or another of the later Civil war commanders, IDK which exactly. If the English can save La Rochelle then the Huguenots would remain a significant thorn in the side of the French Crown, possibly enough to remain a state within a state. I can't see the French getting involved in a major foreign war with a potential fifth column in their ranks. At the least I can see the Huguenot coastal territories emerge as English Protectorates. On the flip side though I wonder how an alliance with Calvinists would effect Charles I's Arminianism religious policies.
As to the Dutch, not entirely sure about the changes there. I don't know as much about them during this point in history as I do about Spain, England and Austria, mainly because they never interested me as much. But an interesting jumping off point would be to have the Dutch fail to capture the Spanish treasure fleet in 1628. That keeps the Spanish more financially stable in terms of credit and keeps the Dutch from being able to take the fortress-city of 's-Hertogenbosch. This keeps the geo-political situation in the Northern Netherlands firmly in favor of the Habsburgs, especially with Breda under their control.
I think the Swedes would have a harder time winning against the Commonwealth than during the Deluges, but I do think that they would end up winning, for no other reason than that the PLC was in trouble with just about every neighbour they had and the Swedes had been building up a incredibly effective military force that was only just reaching peak performance having learned a great deal from previous mistakes. I just don't see the Poles being able to put together anything that could truly compete with what the Swedes had in their arsenal at this point.
I think the PLC in general would be too busy with their encroaching neighbours to try for Prussia at this point. The Russians are never going to cooperate with the Poles as long as there is a Polish claim on the Russian throne and there are simply too many benefits to Russia attacking the PLC to ignore. Brandenburg might, as you mention elsewhere, be tempted to go for Prussia, and if the PLC seems weakened or distracted enough I can see them jumping on the growing bandwagon. This is only if the situation in the HRE permits the Hohenzollerns to attempt this.
Killing of Buckingham would definately be a start and your other suggestions for how that situation would evolve seem like a good way of acheiving the goal you have set. Without La Rochelle's fall the Hugenots remain a major threat to the French Monarchy and they are left almost completely paralyzed, as they had for the last half-century. I don't think the Huguenots would become English protectorates, more likely they are able to further entrench their hard-won gains from the French Wars of Religion. One consideration you might have here is that by having Richelieu fail in this task, he could end up disgraced and lose a significant amount of his influence on events. I am not sure who would pick up the reins with Richelieu in disgrace, but it is hard to imagine anyone truly being able to do as good of a job.
I don't really know the specifics with regards to the Netherlands either. But having them never quite sally forth would be interesting. If you have Richelieu disgraced from the Anglo-French War then you might also want to consider the effects on the War of Mantuan Succession which he was heavily involved in escalating and which stretched the Spanish resources almost to the breaking point.
At this point I think we could very well end up with an early and significantly cheaper end to the 30YW, a shortened or completely butterflied War of Mantuan Succession, a improved situation in the 80YW for the Spanish, a English victory/lack of French victory in the Anglo-French War, and potentially anything from an Early Northern War to an Early Swedish Deluge or Wars of Polish partition (unlikely to go that far in any case, but might be interesting to see what happens if the PLC is dogpiled by Russia, Sweden, Brandenburg, and the Ottomans). I think this might all be very interesting
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Not necessarily. From what I can tell the Imperial army was still much larger than the Liga one (110,000 to 30,000) and if push came to shove the Imperialists are likely to win. How likely are are the Princes to rick a war with the Emperor at this point? I mean the advantage is with Ferdinand II and any who directly attacked him would legally be rebels, subject to the Imperial ban (not unlike the Palatinate). In this case Bavaria basically let the genie out of the bottle by demanding and receiving the Palatinate and its Electorship. But I personally don't see Ferdinand II going to far, just pointing out that if he did, the advantage lays with him.
As for his supporters, they were already in the possess of being rewarded by 1630. Bavaria can't expect much more than what they had, Saxony would still get lower and upper Lusatia, not sure about Brandenburg though. Further Pomerania could be in the cards, but with the POD creating an Imperial Baltic fleet it might end up directly under the Emperor, with lands awarded to various supporters but the Duchy itself remaining Habsburg. Considering Brandenburg's relatively minor role at this point they can't expect all that much. I do wonder if we could see a conversion from the Elector of Brandenburg? Probably not but it could be in the cards if it would help him gain Pomerania.
Finally, to the North and treason. The Emperor was actually doing just that. That's how they justified the transfer of the Palatinate and Mecklenburg: their rulers committed treason against the Emperor and had therefore forfeited their possessions. Of course the real question is the Edict of Restitution. Is it fully implemented or is it modified? Or hell is it withdrawn like OTL?
I wasn't talking about out-and-out warfare, but you might see Ferdinand on the back foot if Saxony or Brandenburg suddenly feel that they might be next. The use of the Imperial Ban and confiscations of rebel territory probably happens, and a significant degree of redistribution is likely to occur. I just think that Ferdinand would need to be very careful about alienating the neutrals or his allies. At this point the war had been somewhat limited in the areas that were affected and the Edict of Restitution seems to me to be more of a stick to hit his opponents with when pushing them into more agreeable positions.
Bavaria and Saxony probably retain the gain they have from the Edict, I don't see the Palatinate being given back to that branch of the Wittelsbachs any time soon ITTL. I am not sure about Brandenburg's religious position, it might go either way depending on how large of an enducement is offered (Pomerania) and what other opportunities present themselves (Prussia), but if either is offered I think we might very well see the Hohenzollerns of Brandenburg go Catholic for a while. Ferdinand will need to get the Hohenzollerns on his side in some way, because otherwise he leaves himself vulnerable in Northern Germany.
I really don't think the Edict of Restitution gets revoked in this case, adjusted and the areas in question might change but Ferdinand has absolutely no reason to withdraw it at this point, and with the way the large German states stand to gain from other land awards I don't see how anyone could build enough support to repeal it any time soon.
What if the Emperor were to call an Imperial Diet and use it as a vehicle to reform the constitution to allow such things to happen legally. After all, for at least a few of my suggestions, the Princes themselves had let already let the genie out of the bottle. They can't claim the Emperor is violating their rights and liberties if they themselves started it. While replacing a Protestant with a Catholic is no doubt a step to far (unless of course its a situation like that of the Palatinate), I can see the Imperial Ban be applied more liberally than before against estates that break the peace or formally ally with foreign invaders/. Realistically the Princes shouldn't object to such consequences for treason. After all, its a standard sentence across the rest of Europe.
As to a return to the status quo, unlikely. Like I said, the genie's out of the bottle: you can't put it back in. I think we'd see something quite similar to the Peace of Prague, just more in favor of the Emperor and some kind of compromise in regards to the Edict of Restitution. Something that allows a case by case situation on the various ecclesiastical estates while still allowing the Emperor to save face. Maybe a new court set up to specifically deal with the Ecclesiastical Reservation cases? Of course the northern Bishopric administrators that sided with Denmark will lose their offices and be replaced by Catholics (this was expected before the Edict and was to be considered acceptable). We'd also likely see the counter-reformation in full force in both Bremen and Madgeburg. Would create tensions in the North but would likely stick, like it did in Bohemia and Austria. Finally, we would see a shift in parts of Northern Germany to favor the Catholics.
Have you considered having Ferdinand try to establish a replacement for The Golden Bull of 1356? At this point, as you mention, the genie is out of the bottle, so there might be a significant degree of interest in establishing a new Status Quo that the Imperials and Neutrals would be willing to live with.
There might just be enough impetus from the instability of the 30YW that something like this might occur. The only real problem I can see is that Ferdinand always seemed a bit ungracious in victory, and might try to exploit the situation for all it is worth. His son Ferdinand III might be a better fit if any sort of equitable agreement is to be established. I think there is a significant danger that Ferdinand might just take that single step too far and have everything collapse (not militarily but politically). Even at the best of times Ferdinand II was viewed as being rather difficult to work with, and most seem to have been rather unnerved by him.