This article presents a triangular theory of the structure of hate and a story-based theory of the development of triangles of hate. Hate is proposed to be 1 contributing cause of many, although certainly not all, massacres and genocides. The article describes why the problem of terrorism, massacres, and genocide is of critical importance to psychology; reviews theories of the instigation of massacres and genocides; and then presents the duplex theory. The role of propaganda and other instigating factors is discussed. The benefits and limitations of the proposed duplex theory of hate are reviewed. Possible remedies for hate also are delineated.