After World War 2, there were hopes that wars would become much less frequent. Sadly, that was not to be — though the wars currently in progress are mostly of a very different kind, occurring within states and of a type for which the UN was not designed. The talk will address two questions. First, what are the bases of these wars at the societal level. Do the causes lie in ethnicity, religion, environmental issues, poverty, greed, or what? Second, what are the incentives for those who fight? War is dangerous and destructive — what induces individuals to take part? In attempting to answer that question, it is useful to think in terms of a continuum from conflicts in which individual aggressiveness predominates to those in which war is best thought of in institutional terms. The important driving forces for individuals vary according to the type of conflict. In aggression between individuals, individual aggressiveness is crucial. In conflicts between groups, group loyalty augments and exacerbates individual aggressiveness. Factors making for group coherence are ubiquitous in humans, and often lead to the denigration of out-groups. The psychological processes involved are important in all types of war. In those cases in which the institutional aspects predominate, individuals see it as their duty to participate — and this includes not only the combatants but also the munition workers and so on. To reduce the incidence of that sort of conflict, it is necessary to undermine the institution, and for that purpose the forces that support it must be identified. They fall into three categories — everyday factors, such as the metaphors we use in ordinary speech, and the way history is taught in schools; medium-term factors, such as religion, ethnicity, nationalism and so on; and thirdly the military-industrial-scientific complex, itself consisting of a hierarchy of sub institutions. The role of education in reducing the incidence of war in the long run will be emphasized.