Nice update - I like it - now onwart to teh Carantian wars

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If I read Ankhs update correctly Britain might have ditched Austria in favor of Prussia on grounds that Austria has become (stayed) a big factor. France and Austria are still not friendly - OTL Austria was in a weak Position, so it allied with fFrance on the ground that Austria Transfers control of the Austrian Netherlands. Austria won't do this here, so competition with France is alive. If Russia had allied with Frederick against Austria and Saxony - an alliance with France might have been conveniant for the Austrians, but not here (I assume)
Hmm, I didn't catch this. A few thoughts here. (ETA: And by "A few thoughts", I apparently meant "a very long essay") One is that there's no way the British will ditch an alliance with Austria in favor of one for Prussia. They didn't do that OTL - what they thought they had accomplished was their long-desired project of recreating the Grand Alliance by being allied with *both* Austria *and* Prussia. They were then astonished and horrified when the Austrians turned around and signed an alliance with France.
It seems to me that what you'll basically get is that when France and Britain go to war in the Americas, the French will attempt to put pressure on George II by occupying Hanover. They're friends with the Wittelsbachs Karl IV Theodor of the Palatinate and with Clemens August of Cologne, who between them control most of the territory between France and Hanover. But Franz Georg of Trier, who is pro-Austrian, controls the main route down the Moselle. The only alternative to going through Trier's territories is to go through Liege, whose bishop is, from 1744, another Wittelsbach, Johann Theodor. But Liege is dangerously close to the Austrian Netherlands. The French probably can't get troops through either Trier or Liege without Austrian acquiescence, or, alternately, riling up the Reich by going through Trier without permission.
So let's say they do the latter (Austrian acquiescence seems unlikely). Franz Georg protests to the Reichstag and to the Emperor (i.e., to Maria Theresa) against the French violation of his territory. The Reichstag will likely be sympathetic, but may not do anything, especially if pro-French types are doing well. What Maria Theresa does is less clear, because I'm not sure what her attitude towards the British would be at this point. George II will have played an important role in securing her husband the imperial crown, but she also won't be eager to get into a war for the sake of French and British colonial rivalries. So let's say both Reichstag and Kaiser make only pro forma protests against the French violation of Trier's neutrality. Or maybe the Elector realizes it's hopeless and comes to an agreement with the French in the face of Austrian indifference. Or maybe the French avoid the problem, go through Liege, and the Austrians don't bother them. Who knows? But if we're trying to avoid a Franco-Austrian war, we pick one of these options.
But then the issue becomes even more acute once the French actually get to Hanover. At that point, George II himself can also protest and demand a Reichskrieg against France. Do the Austrians continue to temporize? This is a very difficult situation, but it seems like the Austrians might be looking to flex their muscles, issue an ultimatum to France to leave imperial territory, and start a war if they don't.
But let's say that the Austrians don't do this. I think for them to basically ignore the problem they'd need some kind of major distraction - a war in the Balkans with the Ottomans? Some sort of intrigue in Poland, or with the Spanish in Italy? I'm not sure. Some sort of issue in the Ottoman Empire might create the fewest ripples? But let's move past it - the Austrians, for whatever reason, don't do anything effective to oppose the French attack on Hanover. Maybe, again, there's a pro forma protest but no effective action.What is George II to do? The French will occupy his beloved homeland if he can't find someone to help him, and the Austrians have abandoned him. So he turns to the next largest army in the vicinity - the Prussians, and signs a subsidy treaty to hire on his least favorite nephew to fight the French on his behalf. Perhaps George II has to promise his ill-gotten gains of 1741 back to Frederick in exchange for his help.
Frederick certainly has no particular reason to be friendly to the French. They didn't help him in 1741, they acquiesced in the loss of his western territories, most of which went to the Elector Palatine, now a French ally. Moreover, since the Reichstag will almost certainly have issued some kind of condemnation of the French invasion, Frederick can claim to be basically doing a Reichexekution, acting in the name of the Reich rather than simply as a mercenary, and winning back some credit in the process.
So Frederick leads his army west, beats the French invaders in a nice set piece battle or two and pushes them back to the Rhine. The French agree to a convention that neutralizes Germany for the remainder of the war.
This leaves Frederick in a much superior position. He's probably won back Minden and Ravensberg; George II owes him big time; and the Austrians will be reasonably pleased that he gave the French a black eye.
Meanwhile, we can perhaps have some sort of tension going on, involving Poland in some way, that leads to poor relations between Austria and Saxony - perhaps this could arise out of whatever crisis Austria is dealing with in the Balkans. Maria Theresa thus seems to be looking reasonably favorably on Frederick, and reasonably unfavorably on Augustus of Saxony.
So now Frederick doesn't need to be quite as insane to launch his attack on Saxony. Maybe Maria Theresa even tacitly encourages him as part of an effort to win concessions from the Saxons on whatever they're arguing about.
I'm still not sure how the Bavarians fit in. Karl Albrecht (who I guess lives longer here out of reduced stress from not becoming emperor?) is still going to be relatively pro-French, and the French aren't going to be either friendly to Frederick or hostile to Saxony (which here is both in difficulties with Austria and likely in a marriage alliance with France.) He's also going to be anti-Austrian, and at this point the Prussian attack against Saxony is one that the Austrians seem to be tacitly supporting. So I'm not sure how this works. But maybe the Bavarians feel abandoned by Louis XV and are trying to strike out on their own. I'm not sure.
So then Frederick attacks Saxony. Likely he does this without consulting very closely with Austria. But Maria Theresa didn't actually want a Prussian invasion - she was just trying to leverage the threat of one into Saxon concessions over whatever it is she's quarreling with Augustus about (some issue with the Polish border? Saxon claims to Lower Silesia? Perhaps she's trying to win back Upper Lusatia? something in the Balkans?)
So Augustus likely first turns to see if the French will help - but I suppose they won't; perhaps you could extend their colonial war with Britain a bit longer so that they're still preoccupied; at any rate, the French aren't in a particularly good position to do anything to help, given the loss of most of the western Prussian territories and English/Hanoverian friendliness to Prussia. And then he turns to the Russians - but perhaps there's internal politics going on there that make Russian help less than forthcoming. And he turns to the Reichstag - which is sympathetic, but not really able to do anything without the Emperor's sanction. So he finally has to go to Maria Theresa. He agrees to whatever concessions she's been demanding and she agrees to help him against the Prussians and Bavarians. Thus, the unexpectedness of her move against Frederick.
So that maybe gets a somewhat more plausible route to what Ankh's looking for?
But Austrian intervention is going to have weird effects in the Empire, since it effectively means Austria is switching sides. Before you had what looked like Britain--Austria--Prussia--Bavaria against Saxony--Poland--France--Russia, or something along those lines. Now you have Saxony--Poland--Austria--Russia against Prussia--Bavaria. Britain and France's positions have been thrown into considerable confusion by the Austrian volte-face. I'm not sure where it goes from there, or if Ankh's idea that Austria could just beat up on Prussia and Bavaria without either Britain or France doing anything to oppose it makes sense.