Use "debug yesmen" if playing with the Hearts of Darkness DLC. This command will toggle "yesman mode" for all AI nations. In yesman mode, the AI will always respond favorably to offers and deals. Note that AI will respond favorably to offers from other AI nations too.
The syntax for the yesmen command is as follows:
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Find below working examples of the yesmen command.
If yesmen mode if turned off (default), typing the above command into the console will turn yesman mode on for all countries, meaning every proposal, offer and deal will be accepted. Typing yesmen into the console when it is enabled will turn it off.