Revisionist approaches to the ethics of war seem to imply that civilians on the unjust side of a conflict can be legitimate targets of defensive attack. In response, some authors have argued that although civilians do often causally contribute to unjustified global threats – by voting for war, writing propaganda articles, or manufacturing munitions, for example – their contributions are usually too ‘small’, or ‘remote’, to make them liable to be intentionally killed to avert the threat. What defenders of this view lack, however, is a theory of causal contribution. This article sketches and defends a theory of causal contribution. We then apply it to the kinds of situation that defenders of the view are interested in. We argue, however, that since degrees of causal contribution turn out to be sensitive to particular features of the situation that are extrinsic to the agent's action, whether an agent makes a small or a large contribution to a threat may not only be very difficult to discern but in many cases may not line up very well with the kinds of intuition about liability that defenders of the view want to uphold.