What dictates when an AI is willing to declare war?

[MyOlde]

Often enough when I want to trade for something, including getting someone to declare war on my enemy, it will be redded out (if there is such a term). If I go to another AI I may find he or she's willing to trade for it. What makes them decide one way or another?

[joncnunn]

I don't have the exact answer; but it has something to do with the relationship between that AI and the one you want it to declare war with.

[snoopy369]

Relationship, existing trades between them, power differential, relationship with you, probably your power ... probably more things i'm not listing.

[Yaga]

Individual leader traits as well. Mansa Musa, for example, will more readily trade techs than others, while Tokugawa usually won't even trade Open Borders until he's Pleased.

[The Priest]

The real rule is:

Do you need the AI to launch a war to help you out in a dangerous looking war against a powerful enemy?

Yes? he won't. No, you have a chance.

[Lancer]

If you get to defensive pact and the AI attacks you they'll join and that can effect those two civs later relationship even if you don't have a pact. Problem is, such pacts come very late imo.

[joncnunn]

Ah, but that is somewhat offset by vassals. I was quite suprized in my current game when Catherine called me up right after I discovered Fedualism asking for my protection. (I guess she really did want CLOSER relations).
So that meant that when De Gaul declared war on the Korean civ, I was able to successfuly intervene on the side of De Gaul (asking waiting for him to ask for that help) while Catherine watched my back. I only had to take two of the Korean civs cities to get them to capitulate.