Larmantine said:There's not. Well, looks like just gonna wait for a war.
Not sure if it works in diplomacy, but in native you can demand tolls from caravans to put you at -1 relation with said faction, then besiege and capture a city. Have only done this once, but soon after Vaegirs declared war on us. No honor loss or relation with king loss.
Misc. question, but are lancers considered heavy cav?