This is a major issue for me ,i try to role play and as a part of it i never declare war, with exception being when i want to recreate some historical wars like Punic , etc , instead i let AI to build up and comes after me . This is how i always played since original Shogun.
It is extremely frustrating when AI hate your guts and has similar size empire and does nothing. I have sink somewhere around 800+ hours in this game and had only maybe few times AI declaring war on me past turn 50+. And even when it does there is no AI army anywhere near my territory, so i can assume that war declaration was one of those random ones that have chance to occur on every turn (there is a value in db tables for that).
That just never happened in any previous TW game , going from Shogun to Shogun 2 and it's very disheartening.I don't know if CA hardcoded anything , but Rome 2 CAI is complete;y harmless and neutered,IMHO