Tribute

[bs_grom]

It would be great if during a peace treaty one could demand a tribute from a defeated country for a certain number of turns.
As Rome did, when he defeated the enemy completely but did not want to destroy him, but weaken him so that he would not threaten him in the future, i.e. imposing a high tribute and military restrictions.

[Southern Hunter]

Sounds good

[Pocus]

It was planned but it demanded some changes that were not trivial. You can at least demand an instant tribute, so it is close to that.

[bs_grom]

Similar but there is a difference.
Vassal cannot declare war or sign peace alone.
Maybe the word tribute is not appropriate. War indemnity would be appropriate. If it was large enough that the country does not have such a sum, it would be spread over more turn. There are two well-known cases from history. After losing at Magnesia, the Seleucids pay huge contributions, lose the provinces of Asia Minor, and eliminate elephant units.
Carthage loses Sicily after the First Punic War, pays compensation.
Both countries continue to pursue independent policies but are weakened.
After the Second Punic War, Carthage pays compensation, loses Spain and has a limited fleet. I meant it.