AI vassalises to strong opponent to bribe him into war

It happened to me in several games. I was in war with Tokugawa or other AI, he was already crippled, but he was still refusing to capitulate. Instead of capitulated to me, he become vassal of somebody else, who was not originally involved in the war and who immediately declared war on me. Is there any way, how to prevent enemy from vassalising to someone else in these situations?
Can all of the AIs act this way or only some of them are coded to this behavior. It seems, that for example Tokugava often tries to find any way to avoid capitulation to player.

Beg/demand 1 gold from the powerful civs once your target is on the ropes--they won't be able to declare on you for 10 turns, and therefore won't be able to accept a p-vassal that's at war with you.

Lennier said:

Beg/demand 1 gold from the powerful civs once your target is on the ropes--they won't be able to declare on you for 10 turns, and therefore won't be able to accept a p-vassal that's at war with you.

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Sometimes strong oponent refuese to give you even 1 gold.

If they are pleased with you and you haven't begged anything from them in a while, then they won't refuse. I don't think their strength has any influence on the decision when you ask them nicely.

capitulate confuses me. sometimes when i capitulate someone, the other civs immediately declare peace and other times they declare war. i'm never quite sure which one it is going to be. and when someone capitulates a civ i'm at war with, i have no choice but to go to peace for at least a turn, usually sending my army 5-15 squares away. one time my army went back to my original continent and it took me 20 plus turns just to reach the continent i was just on.

things that are also slightly annoying are that if a civ has a vassel, it is so much harder to get them to capitulate, even if that vassal is super weak. and when a civ doesn't capitulate when it gives the excuse, " we are afraid of your enemies." this coming after i have already taken 10 plus cities and my power graph is infinitely stronger than said enemy. shouldn't the big stack sacking city after city on the verge of killing off empire be the person you are afraid of.

elitetroops said:

If they are pleased with you and you haven't begged anything from them in a while, then they won't refuse. I don't think their strength has any influence on the decision when you ask them nicely.

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This is true, and even for demands they only refuse if they have 4/3 times your power, aside from the same exceeeding quota and beg memory mechanics that Pleased+ begging suffers from.

el toro loco said:

capitulate confuses me. sometimes when i capitulate someone, the other civs immediately declare peace and other times they declare war. i'm never quite sure which one it is going to be. and when someone capitulates a civ i'm at war with, i have no choice but to go to peace for at least a turn, usually sending my army 5-15 squares away. one time my army went back to my original continent and it took me 20 plus turns just to reach the continent i was just on.

things that are also slightly annoying are that if a civ has a vassel, it is so much harder to get them to capitulate, even if that vassal is super weak. and when a civ doesn't capitulate when it gives the excuse, " we are afraid of your enemies." this coming after i have already taken 10 plus cities and my power graph is infinitely stronger than said enemy. shouldn't the big stack sacking city after city on the verge of killing off empire be the person you are afraid of.

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Capitulation and Peace Vassal mechanics are diferent.
Capitulation can only take place between warring civs, in the case of capitulation all wars against thecapitulated target immediately cease.
If a civ peace vassals to a third party who they are not at war with however, the new master must declare war on everyone the vassal was at war with.

Also one extremely annoying condition on AIs considering either vassal type is that it must have lower than than the worlds average power, tiny vassals drag this down badly to the point of the existance of a single 1 city vassal anywhere in the world basically prevents any more vassaling

In war, vassal inherits master's wars; while in peace, master inherits vassal's wars

thanks for the advice