AI willingness to join wars

[Sharpie The Dragon]

I'm playing a game as Etruria on 1.31.6.0. I'm allied with Austria, Ottomans, Papal State, Castile and Savoy. I want to declare war on Venice with conquest CB. I can call Savoy and Austria into my war, I also want to call in The Papal State but there is a -100 penalty for "Accepting would destabilize The Papal State" - Presumbly they will lose -2 stability since both nations have +200 relations with each other, they are not allied, they have no truce, also attitude towards enemies is -60 for The Papal State.

However, what I do not understand is that if I set the nation of Trent as a co-belligerant, The Papal State is now inclined to join, the -100 and -60 penalties are magically removed. Upon testing and declaring war with Trent set as a co-belligerant as well, The Papal State doesn't lost 2 stability.

So what's going on here in the calculations that I'm failing to understand? How does the nation of Trent have any impact on Papal State willingness to join a war? How is the nation of Trent causing The Papal State to not take stability hits?

https://steamcommunity.com/sharedfiles/filedetails/?id=2630584731

https://steamcommunity.com/sharedfiles/filedetails/?id=2630584931


I can do the war easily without Papal State assisting, I'm just merely asking.

[Marcos_DS]

Setting someone co-belligerent will add extra incentive for the AI to join wars. E.g. attack portugal and france isn't interested. Attack Portugal and set England co-belligerent and you are good to go.

With the exception of truce which seem to be hard limitations for the main war goal (won't join wars if they have a peace deal, even if you set others co-belligerent), it seems you get a kind of "best-off" deal with the modifiers choosen "best off" from all co-belligerent enemies.

Edit: That said, this is anecdotal - if anyone knows the exact mechanics i'd also be interested to know...

[Vetgirig on Linux]

Co-belligerent is seen as someone you would take provinces from.

If they want some of that nations provinces - or is that nations rival - they will join.

[salatrin]

It also works the other way too. You go to declare war against an enemy and one of their allies wont join in against ya for whatever reasons, but the instant you click the box to call in one of your allies in the declare screen, the nation previously not wanting to join might then think...ohh you calling in that guy? ohh i hate that guy, I change my mind, i want in.

In those cases, it best to avoid calling in your own allies till AFTER the war has been declared, and the enemy ally who didnt want to join has already refused and lost alliance, then once the war has started, call in all your allies.