Quote Originally Posted by Kobal2fr
"If they have more than 3 times as many men as us on their frontlines, and their total strength is more than twice ours, and their economy is much better, and they're our strongest neighbour, then raid and want_allies_against_him".

Now, don't take this at face value, because obviously it's a low priority decision, and the AI will deal with more pressing matters first... but nevertheless, it's geared to annoy the strongest around if possible and there's nothing else to do/no other war going on.
Of course if you have a neighbour 3 times more powerful you'll want to divide et impera on him and try to make the world go against him (even if he's not your direct neighbour).

Quote Originally Posted by Kobal2fr
It's not suicide, it's just the only thing they can do to fill the gap between you and them. If they didn't they'd just be waiting to be steamrolled. Commenting out that line should make them stay put when completely overpowered, but since the player is number 1 very easily, it might make every other faction very passive towards you, which is a bad thing.
That depends from how deep is the gap to fill (sometimes, it's hopeless); in my games, I try to imagine what I'd do if I was a 2-provinces-left faction bordering with an empire with 30.

The first priority is not to make him smaller, the first priority is "survive; make the things the way he'll never attack us until we have rebuilt a decent kigdom by foraging on other factions, no matter if you have to become his vassal, no matter what you pay; we must be on his side or remain neutral, or it's game over".

That would maybe prevent the small faction to be steamrolled, at a cost of being more passive towards the Player's Empire, but that is what would be logical.

Of course you can say too much logic ruins the game (or make it end prematurely), but that's what the Glorious Achievements were for in MTW: the chance to "win" without having to conquer the entire world as the only option.

Btw faction were more passive with Glorious Achievements, but nonetheless they battled with assassins, inquisitors, religion conversion; more passive only in military sense.