Professor Thomas Homer-Dixon gives a talk on Dehumanization for the Oxford Martin School Public Lectures series. Introduced by Professor Ian Goldin. Dehumanization is arguably a defining feature of the most brutal acts of human violence, such as saturation bombardment of civilian populations, terrorist attacks on urban centers, intense battlefield combat, and genocide. I propose a psychological explanation of this phenomenon that uses a catastrophe manifold to describe a set of psychological states in an individual's mind and the possible pathways of movement between these states. The manifold exists in a three-dimensional phase space defined by the variables identity, justice, and structural constraint. It specifies five hypotheses about the causes and dynamics of dehumanization. Taken together, these hypotheses represent an overarching theory of the nonlinear collapse of identification at the level of the individual.