This is the one reason I'm giving this game a few months before I inevitably get sucked back into singleplayer, only to be burned out after the 5th cookie-cutter quest/battle.
providing the player with proper information should be much more doable.
To add these little things that inform the player "why", I'd absolutely hate to see another notification popup GUI implemented. I'd much rather have a messenger party find me on the campaign map, or learn something by talking to a notable or towns-person.
That said, there are a ton of things in-game that have a dedicated GUI that would be really cool if they didn't.
Like voting: warband had a really nice system where you could convince other vassals to vote for you or your choice in terms of fief ownership, with relation gains and penalties. I was dissapointed to see that simplified into a single screen that decides everything.
Same thing should be for war: it's another vote, it can be reconstructed into the same warband system of trying to get all the other nobles to agree on a 'yes, war' or 'no war' standpoint. THEN have the "official" vote screen popup, if we must have it.
This way, if a noble needs convincing for or against a kingdom decision, they could assign you a
short quest (or at the very least, a persuasion dialogue) that would help align them with your view. Then you'd know why they're voting for or against you; because you were involved in their decision making process. (Fail the quest, they carry on against you, etc)
This sort of thing should be available for you to use/exploit whether or not you are a part of the kingdom or not... If you are part of the kingdom, you may have a good chance at persuasion. If not, then maybe the noble gives you a quest, with a scaling difficulty according to your renown and relation with the noble. This way you can convince both your own kingdom and another's kingdom to avoid war, for example, by listening to their concerns and finding a solution through questing/persuasion.