Civilisation is not possible unless aggression can be brought under control. It is armed aggression - aggression by governments and by groups that hope to become governments - that most strongly threatens human survival. About this, Freud's theorizing most strongly captures the imagination. Professor O'Brien begins with a persuasive account of this theory, brings out its importance, and suggests lines of exploration. There are four problems with Freudian explanation: Freud's theories explain too much and therefore explain nothing; the logic of claims about unconscious motives poses difficulties; Freud uses tautologies as explanations; Freud stretches concepts like that of desire. This paper explores these problems and then takes up O'Brien's other suggestive analyses.