War is not just about death and destruction, it also causes long term damage to the health of nations. Trauma caused by the experience of conflict has a profound impact on mental health, often persisting even after the fighting has stopped. It can cause depression, anxiety, post traumatic stress disorder (PTSD), bipolar disorders and schizophrenia. People who have lived through conflict are more likely to be diagnosed with a mental illness, and that can be passed down through generations.

In addition, the economic pain of war impacts all citizens. The $1 trillion worldwide economic losses incurred by war have far-reaching effects on communities, including the loss of schools, factories, roads, hospitals and more. The result is that people are unable to build secure lives and their communities are weakened, with less capacity for growth and development in the future.

The underlying reason for many wars is greed. Countries want more of everything for themselves, whether it be food, mates, gold or land. Religion is sometimes used as a cover for this lust, but the core motive is usually to have more power and control over others. This can lead to a Malthusian world view where the population is growing faster than the resources, which creates a scarcity that triggers violent conflict.

Another cause is the need for revenge, which can arise when one country feels that it has been unfairly treated by another. This can be because it has been robbed of some resource, or because of the failure of negotiations, or because of an “irreconcilable difference” such as ethnicity or religion.

A third reason is that of necessity. It may be necessary to defend the country or its citizens from an enemy attack. It might be a matter of life or death, for example if the country is attacked by an atomic bomb or a chemical weapon. There is a need to respond as quickly as possible to save lives.

All of these factors, however, must be seen as interconnected within a social field that is constantly evolving. The conditions that make war possible, therefore, must be understood as a dynamic process, not simply as a linear sequence of causes. This understanding will allow us to develop new ways to understand and prevent wars. It will also allow us to move beyond a view of war that is restricted to conflicts between States, to include non-declared actions and ritualistic, culturally evolved wars such as those in which Genghis Khan led his mongol tribes across Asia and Europe.