Whether war is defined as organised large-scale violence, coercion or a state of hostilities, it is inseparable from the physical destruction of human lives and environment. It is also a state of fear and tension between opposing forces. Many civilians suffer psychological trauma as a result of the conflict and can be affected for years to come.

The origins of war are complex, and there are many different theories of why people fight. There are two major schools: those that attribute the causes of war to specific innate human drives, and those that relate the causes of war to certain social relations and institutions. The former include ethologists, who make analogies with animal behavior, and psychologists and psychoanalysts. The latter include both optimists and pessimists concerning the preventability of war.

There are several factors that lead to war:

First, there must be a disagreement between states over some aspect of world politics or international order. This can be a question of economic policy, cultural values or the size and scope of government. For example, the American Civil War arose from long-standing disputes between Northern and Southern states over the economic policies of the Federal government, the role of slavery in American society and the extent to which the Constitution allowed the Federal government to restrict state rights.

Second, there must be a perceived need to protect one’s own territory, interests or security. This is the core motivation behind most military campaigns. The need for security is typically stronger in developed nations than in developing ones, where there is less of a safety net to fall back on. Third, each potential combatant must believe that they can win the war in the way they define victory. This is a combination of the desire to achieve their war aims (desirable slice of territory; defeating the other) and their belief that they can do so without significant cost to themselves or others.

For the most part, political leaders and the public do not appear to be particularly eager for war, unless they are convinced that there is no alternative. Even then, there are exceptions to this rule. President McKinley, for instance, was led into a war with Spain in 1890 by the popular enthusiasm for such a conflict.

The long-term effects of War are devastating to both soldiers and civilians. Soldiers often have to live with physical injuries that affect them for decades, while civilians must learn to live with ongoing fear and a sense of insecurity in their daily lives. The fear caused by living in a war zone can have lasting health consequences, including depression and anxiety disorders. In addition, civilians can become sick from the lack of food and the stress of being uprooted from their homes. The mental health impacts of war are a serious concern that must be addressed. There are a variety of ways to help mitigate the effects of war, both for those fighting and those who experience it as a victim.