i'm playing as belgium and early in the game i took two states from the netherlands. now, ever five years to the day they see fit to declare war on me to retake these states. i beat them handily every time, but can't make them a puppet without a large warscore, which would require me to invade in southeast asia, a costly and frankly somewhat dull proposition. how else can i get them to stop declaring on me and just settle down? having to deal with them twice a decade is really sucking the realism out of this game.
I'm not sure if you've got vanilla or AHD, but you don't really have much recompense, apart from actually taking more states from them (if you can). Maybe use a cut down to size war goal to cripple them for a longer period?