So here is a case where I think the AI behavior is irrational.
Now Siam has been a rabid dog all game. He attacks, peaces, attacks, peaces...alllllll gaaaaaame long. And never once has he made a dent against me, we both just drain each other and then peace out.
So though that was highly annoying, ok even though we have the same religion you hate my guts for some reason this game, got it.
But now I am fighting Morocco, who is just 5 votes from winning Hegemony, with 6 turns until the hegemony vote. I am not winning in any category, Siam himself is now outteching me, and we both have the same Ideology.
and yet Siam takes a bribe to go to war with me....it makes no sense. He can sit back, let me exhaust myself on Morocco, kill the threat, THEN try to pounce on me.
And I'll note I'm wondering if this is an effect of some of the flavors, as I've noticed this "dog with a bone" behavior from Siam in other games. It feels like once he hates you, he will not rest until he has removed you from the earth, no matter how many turns go by.