Went bankrupt as Ireland once. Stupid Castille took over the warleader and, since I was the wargoal, I couldn't make peace. Had to sit there with all of my provinces occupied while Castille just farted around getting its navies destroyed for like two years.
In times like this, I could swear the AI is trolling you.
As a player in charge of a war, you can usually recognize pretty fast if a war can only go south for you. With that in mind, I'll usually be happy to offer concessions early on
before my army and manpower are both gone and I'm being carpet sieged because the AI will be more willing to listen to lesser concessions when it still has to actually beat you. Once you're beaten, then there's nothing stopping them from pressing further and for more.
Enter the AI becoming war leader against an enemy it has absolutely no chance to beat. Recently had a situation where Denmark called Poland in a war who in turn called me (Hannover) into the war against Sweden and Great Britain. Denmark got squished, with the naval superiorityon the enemy side there wasn't any realistic way to get to Sweden, Poland didn't actually seem like it wanted to march over to the fighting...
Leaving me getting overrun by the Swedes and their massive discipline and duo of five and six shock generals. It's like "Poland, c'mon guys, there's zero chance we win this thing. Stop being dicks and just give Sweden what they want."
Given that even decades later we still have close ties, I don't think it was a purposeful "sabotage our allies" move on Poland's part: they were just too dumb to realize that with every passing month Sweden was expecting to get more and more out of the war
and Poland's strongest ally (me) was taking a serious beating which in no way actually benefits Poland.