That is a large enough empire that you should not have yielded anything, you could have worn them out.
But at what cost? Poland looks super stronk and might have invaded once the military exhaustion and casualties went up.
It's a tough one to say not knowing more than what is in that screenshot. The overall warscore is +2 and there is over 40K manpower left (and about 170K troops in the field according to the sidebar), which suggests playing a cautious defensive strategy and holding out for a white peace (particularly as defending Istanbul will give warscore over time), at least, should be feasible, even if an offensive strategy would result in too many losses. But the opposing forces may be stronger yet - especially if France has near maximum manpower - so cardgame's point about potentially overextending is a valid concern. An invasion from the Commonwealth could transform that nuisance war to a crisis. I probably would have tried to peace out with Genoa and end the whole thing, though, rather than Venice alone. Though perhaps Genoa would have demanded far more. Perhaps the most concerning is the lack of allies. In a defensive war, there should be more than one ally, preferably including at least one decently strong one. Spain would be ideal, Great Britain pretty good, and the Netherlands and Denmark would be nice. But in the end, even one of them would have decreased the chances of Genoa starting a war, and also would decrease the chances of overextension and the Commonwealth invading even if Genoa had still started this war.
So I started a new game as Austria, and I'm not quite sure where I should go from here. I feel like I've had a relatively successful early game, taking out most of Venice and a good part of Southeast Europe, but I'm not sure what I should do now. My imperial authority seems to be shrinking, and I lost recent alliances with Burgundy and Bohemia. Is it a good or bad idea to expand by conquest within the HRE? I had the shadow kingdom event trigger because I forgot about Italy.
I think its a waste to go for germany. Try rather taking stuff elsewhere while building imperial authority, so that the empire provinces gets developed without you having to spend on it
No longer be Emperor? If you can't bribe them and/or they already hate you, you don't have many options. This issue may also be part of the Wars of Religion event chain, where you are forced to lose the throne for at least one ruler, but you can generally regain it afterwards.
Expanding by conquest within the HRE gives more aggressive expansion within the HRE, which makes it less likely to be elected, and having unlawful territory also hurts HRE relations, which makes it less likely to be elected. So generally, yes, expanding within the HRE is not a great idea if you want to be Emperor. You can get away with a little bit, but not with a lot. Although I should note that the most recent time I played in the HRE and tried to be Emperor was as Saxony in patch 1.5, so my feel for how much you can expand is likely out-of-date. There is of course the option of to expand within Germany and not care about not being Emperor. It's still an interesting area to play, with so many small countries and the HRE mechanics in play. I had two good games in the HRE or HRE-area while not trying for Emperor.
Also what should I do about all the Protestants within the HRE? Having so many heretic princes is really hurting my imperial authority. I was able to stay emperor by improving relations with some electors. Is trying to get provinces to return unlawful territory a good or bad idea?
You could try it. At some point, though, the Wars of Religion will kick off and then it gets really interesting.
I lost the war of religion and now the HRE is Protestant. Is there any way to regain the title of emperor as Catholic Austria?
In the Sikh Delhi game I am playing, every elector and free city was Protestant, alonf with most everyone in the HRE. Unfortunately for them, Russia, Ottomans, Austria, France, Spain and Great Britain were all in the Catholic League.
I tried that but now Hungary and Bohemia both hate me, and Bohemia is growing. So I can't move troops between my Polish exclave and my main territory. I'm going to have to take one of them on at some point, but they both have allies, so I'm not quite sure what to do. That would be difficult, because the Protestant league had over double the military strength of the Catholic league. I'd probably have to go pretty far back and try to run my diplomacy differently. My annexing Wurttemburg is what seemed to trigger the war, so maybe I could have just not done that and hope to avoid war entirely. This is what it looked like before the war. I lost some territory to Burgundy, the Ottomans, and Lorraine, and took over more of Commonwealth and most of the Teutonic Order after the war.
...well, I shall point out you totally failed at being Austria. Like...No PUs as Austria, who can get Bohemia and Hungary to basically just be handed to you? No trying to force the Burgundian Succession so you own the Low Countries? No wonder you were having issues. Literally half the strength you should have is literally not there under your heel.
In response to the classic question of, "how is your EU4 game going?", my current answer is, "it's about to get real!" My Swedish strategy has been largely focused on the Danes, and following that (they are all but conquered), on northern Germany, with the goal of being the dominant power in Lubeck. It has worked quite nicely; I have 44-50% of the power there, and combined with another 40% in the Baltic, has been a boon to the Swedish economy. It's now been about a decade since I took Verden (whose only remaining province is Dithmarschen) and Stade, and a few countries had left the coalition, so I thought I might be in the clear. Turns out, Friesland disagreed. My insurance-ally of the Ottomans declared war on the Mamluks, and next thing you know Friesland declares on me. But despite the 17-country coalition, it should be a doozy. The forces are quite evenly matched: Granted, the Ottomans have two wars, but I still expect a close battle. I have forts in Denmark that should bottleneck the invaders nicely and allow a nice, slow defensive strategy until the Ottomans defeat the Mamluks. Only real question is how much to try to save Mecklenburg and Hesse. Mecklenburg is an old friend, though also my main trade rival in Lubeck; Hesse's main role as an ally was to prevent them from joining the coalition. But it's been a fun time. From economic uncertainty and relying on help from Novgorod and Lithuania to defeat the Danes and Norwegians, to economic prosperity and now this challenge from the south. Meanwhile to the east, Novgorod and I just humiliated Muscovy, who has major rebel problems and wars with all the hordes, which they are losing, so that front is secure for at least another decade.
How are you all feeling about EU4 atm? The insane amount of blobbing that the AI has begun to do (in most of my games, Spain has swallowed France or the reverse) is incredibly immersion-breaking. Like playing Civ sometimes, with the lack of ebb and flow.