@Jellybug Spoiler : Peace vassal fairy is not completely random. You can check the diplomacy screen every turn to see if your enemy is willing to put capitulation on the table. If they are, then that means they are ready to become someone's vassal. In this case I was committed to finishing them off to avoid motherland happiness penalties but it wasn't entirely unexpected. @prettification Spoiler : I am not a fan of keeping vassals on prince difficulty. I only do it for domination victories on immortal/deity because your vassal, with AI bonuses, will easily out-produce you, making them an invaluable war ally for the rest of the game.