The study of war is an important subject in its own right and has been the focus of extensive research and writing throughout the ages. Endeavours to understand the nature of war, to formulate some theory of it, are of enormous significance because they shape human expectations and determine human behaviour. Theories are not only analytical, but have a strong normative element that tends to direct policy and prevent war. There are numerous schools of war analysis, ranging from philosophical to economic, technological and legal, but most include a blend of analytical and normative elements.

A central issue in the study of War is the question of definition. As with any social phenomenon, there are many different approaches to its definition. The student of War should be careful to examine the proposed definition, because it often masks a particular political or philosophical stance paraded by the author. This is as true of dictionary definitions as it is of articles on military or political history.

Many theorists have attempted to define War, usually in a way that distinguishes it from riots and rebellions, or metaphorical clashes of values. Some theorists have gone so far as to deny that war has any rational character, arguing instead that it is a calamity and a social disaster that should be avoided.

Another approach to defining War is to use quantitative methods. One of the best known is the Correlates of War data set, which defines a war as a violent conflict between two states that results in at least 25 battle-related deaths over a period of a year. This definition applies to both state-based armed conflicts and non-state-based armed conflicts (e.g. terrorism or separatist movements).

It is also possible to define war in terms of the territory involved. For example, the Uppsala Conflict Data Program and Peace Research Institute Oslo have defined a war as a territorial dispute that involves at least one de jure or de facto member of the United Nations. This definition applies to both state-based and non-state-based armed conflicts, including de facto states such as Taiwan.

Children in war zones suffer in a variety of ways. They are directly exposed to violence and the effects of war on civilians, they are often drafted into fighting forces or into sexual slavery, and they can also become victims of landmines or other weapons. They also carry the emotional trauma of their experiences, a burden that can be especially heavy if they do not have a support system to help them through this time in their lives.

In the long run, the indirect effects of War are also devastating to societies and to humanity as a whole. For example, the devastation wrought by war can divert resources from the economy, reducing its productivity and putting economic growth at risk. This, in turn, can reduce the quality of life and lead to poverty, unemployment, social disintegration and crime. Moreover, the environmental damage caused by war can cause irreparable harm to the world and future generations.