Firestone, R.W. (1996). The origins of ethnic strife. Mind and Human Interaction, 7(4), 167-180.

Ethnicity and ethnic wars are related to the attempt to defend against emotional pain and death anxiety.  Psychological defenses formed originally to cope with childhood trauma are reinforced as the child becomes aware of death’s inevitability.  These defenses become an imaginary survival mechanism for the individual. Social systems represent a pooling of these individual defense mechanisms as they are projected into a cultural framework as mores, traditions, and secular religious beliefs. People have a strong stake in their particular world views, feel threatened by other groups manifesting other beliefs, and will fight to the death to defend their point of view. The author contends that the terror surrounding the inevitable end of existence as one knows it drives individuals to merge their identity with the group and challenge, attack, or otherwise attempt to eliminate people of different persuasions.  The outgroup is seen as peculiar, impure, or evil because alternative systems are perceived as a threat to their own symbols of immortality.