It is necessary, psychologically, to so categorize the enemy if it is to be possible to engage in warfare or otherwise violate the generally accepted norms of behavior regarding one's fellow man.
Enemy images are usually black and white.
This means that people or groups who tend to be aggressive or selfish are likely to attribute those traits to their opponents, but not to themselves. This improves one's own self-image and group cohesion, but it also escalates the conflict and makes it easier to dehumanize the other side. While the formation of enemy images is very common, it is a dangerous process that becomes especially so when it reaches the level of dehumanization. Once the enemy is considered to be less than human, it becomes psychologically acceptable to engage in genocide or other atrocities such as those that occurred in Rwanda, Cambodia, and the former Yugoslavia. This is a short summary of one attempt at intervention in Northern Ireland which focused on teaching children to reframe conflicts and to revise their images of each other.