*Character/Family 'Philia/Phobia': It would be a trait that modifies international relations when this character is ruling a country. This trait can be possitive (i.e. Phillia-friend of Carthage) or negative (i.e. Phobia-enemy of Egipt). Some historical dinasties or families should have a permanent philia or phobia that affect all its members: Ptolemaic Egyptians should hate Seleucids and viceversa, for example. I'd call them familiy philias or phobias. Other characters may get this trait as a result of events, diplomacy or intrigues, those being individual philia/phobia.
This would make more relevant who's ruling the country, and intrigue can be used to affect external politics this way... assasinating the only heir of that dinasty that hates your country so it's replaced by other dinasty with whom you can make treaties, boost the career of this guy who likes your country... things like this.
Effects of Philia and Phobia:
-When a character with a phibia/phobia rules a nation, the annual diplomatic relationship change with that country is modified possitively if he has philia or negatively if he has phobia. In the case of being 'enemy', diplomatic actions with that country are harder to succeed, specialy military ones (alliances should be almost impossible).
-For no-ruler characters it should modify their diplo/intrigue chances when sent as emissaries.
Individual philia/phobia: Those does not affect all members of a family but individuals, as a trait. The possitive trait could be get when being succesful in many diplomatic actions in a country, when liberating other country's province... The negative trait could be get when failing many diplomatic actions in a country, when fighting other nation's troops many times, when being object of assasination atempts.... These individual philia/phobia traits should have a chance of being inherited (the romans helped my grandaddy a lot, i like them).
This new rule would be accompanied by a new intrigue option: 'secret donation'. This would use treasury money to increase a national or foreign character wealth and popularity when succesful (the money is suposed to be to boost its political career), but if it fails and its discovered it can actualy lower its popularity. A success in using this intrigue action with a foreign character might give him a phillia trait towards your country.
*Assasination attempts should cost big money