Collateral damage was originally applied to damage to civilian lives and property in the course of a battle. New and different modes of conflict over the past half century have extended the battlefield into more areas than merely front line conflicts -- as seen in guerrilla or asymmetric warfare. Should the doctrine of collateral damage be expanded or restrained in these new contexts? If so, what moral limits should be imposed on defensive or preemptive military actions in these new contexts -- and why?