Agreed! fully should be just that.. as long as we honor alliance should be no issue..  simple fix is before an attack can be made on any ally tiles, alliance must be broken which forces all units from former ally's land before allowing attack.. another method to prevent the ally rush ( where we ally with nation only to move troops to attack close to capital) add a negative modifier to future alliances call it diplomatic reputation you can use this for any abusive or negative act to make future negotiations with all other kingdoms difficult.. if this is not already in there heh heh

Yeah, if you break an alliance or attack under "non-aggression" you should lose a bunch of relations with everyone so they don't trust you or possibly declare war on you (if its low enough). That's certainly workable with the game's diplomatic system.