Why the AI capitulates to other empires?

[TaPele]

Title. I am engaged in a war for several turns and just when the other empire is about to capitulate, it does so but to another empire.
For instance, in my current game, I had been in war with Japan for several turns. Took his capital and capitulation was still in red. Every time after that, I checked and time after time it kept in red as my army moved to the next city. One turn I checked, he still refused to capitulate. The next turn after that he capitulated and became Montezuma's vassall.
IIRC Tokuwaga is one of the leaders that most refuse to capitulate, that's why it took so long I guess...
But, why they do not capitulate to me? Am I doing something wrong?

 

[AcaMetis]

Assuming that Monty was (initially) not involved in this war on either side, I think the most likely scenario of what happened is that Toku bribed Monty on you in return for becoming Monty's vassal. This isn't the same as Toku capping to Monty I believe, so the requirements are different, meaning it can happen even when Toku isn't willing to cap. The way to prevent this from happening is the same way you'd prevent other AIs from being bribed on you - if the AI likes you enough to not be bribed on you this cannot happen, if the AI doesn't like your target enough to take him/her as a vassal they won't accept the bribe, if you have a peace treaty the bribe can't happen, etc.

 

[lymond]

The bottom line though is that an enemy cannot peace vassal to another AI if they cannot declare war on you. That could be a peace treaty, or simply the fact that an AI won't declare on you at Pleased. Monty is not a great case in point on the latter since he will, but you still might have gotten a peace treaty with him. When at war, always be aware of AIs that an enemy might peace vassal to, or in the case of actually being at war with the AI, might capitulate first, which in part is due to war success.

 

[ArchGhost]

OP were you in a joint war with Monty as your ally against Toku?
The AIs tend to cap to each other much more readily if other AIs have the war success against them already needed. I've had joint targets cap to an ally losing no cities at all to them, several times. It's a gut-punch to do all the lifting in the war just to lose the vassal as your prize.


If Monty was indeed not in the war at all and DoWed you over Toku's capitulation to him, it's a cut and dry peace-vassal, which is preventable by maintaining diplomatic relationships above the DoW threshold of any potential masters -- or just force a peace treaty out of anybody who can declare on you. The little guy is a sitting duck then.