War is the violent conflict between nations, states, and non-state actors. There are different approaches to war. These include legal, technological, psychological, sociological, and philosophical. However, no single approach can adequately describe war.

One school of theorists attributes war to the psychological and social nature of humans. Psychologists and ethologists have developed theories based on innate drives and behavioural factors. In addition to these innate psychological and social traits, societies have a variety of ideological incentives to promote and impede peace. Examples of these incentives are freedom, glory of God, and nationalist vision.

A second school of theorists attributes war to social and political structures. This includes the power of the state, social institutions, and the economic system. Regardless of the factors attributed to war, it must be noted that the costs of fighting are high. Since war is costly, leaders often have strong incentives not to escalate. For example, the destruction of a physical infrastructure and the lack of water and food for a population can persist for generations.

Similarly, a breakdown in trust between a group of people can lead to the breakdown of normal human relations. Although this is not the only factor that contributes to war, it is one of the most important.

Lastly, the rise of civil wars can add to the impact of war on the lives of civilians. The majority of civilians in modern conflicts are women. Unlike professional soldiers, women are more vulnerable to violence. They also experience greater levels of stress, which can lead to a loss of self-esteem.

During the twentieth century, more research was done on war. New histories were written and social science identified correlations within datasets. Nevertheless, the majority of actual theories were mixed, as war is a very complex social phenomenon.

The Western tradition of war can be traced back to the writings of St. Thomas Aquinas and Saint Augustine. Various forms of war were discussed throughout the centuries. Following the end of the wars of religion, wars were fought for the interest of individual sovereigns. After the French Revolution, war was expanded to include ideals of revolution.

According to Clausewitz, war is a continuation of politics by other means. This is because a nation can only project its power when its will is consistent with its will. By imposing its will on others, it can limit the dissonance between its will and the will of other actors.

Wars also have a significant global impact. The September 11 terrorist attacks altered the way people viewed war. Many people have questioned whether war is an appropriate method for ending suffering.

The most common definition of war is armed conflict between states. However, the term is used to refer to both international and international wars. Non-state actors can also use military force, including criminal networks and transnational gangs.

While the cause of war is often unclear, it is clear that it affects millions of people. During war, the rights of minorities and refugees are greatly diminished. Children are especially vulnerable and suffer from decreased access to education, water, and health care. Moreover, war leaves destruction in its wake. It is also more expensive than politics. Therefore, it is essential to ensure that war is a last resort.