War is a violent conflict between states or other political entities and is an important part of international politics. War is often unpredictable and the causes are complex. It can take a variety of forms, from civil wars to insurgencies and from interstate conflicts to global crises. It is always a dangerous activity for all involved and can have major economic, social and psychological impacts.

One of the most important functions of war is to provide an opportunity for countries to demonstrate their military strength and to settle differences. Wars also allow countries to pursue their strategic interests and to change alliances and coalitions. Nevertheless, there are many reasons why wars can be unpopular and people may not wish to see their country engaged in conflict. The use of weapons of mass destruction has brought a new dimension to modern warfare.

In recent years, there has been a shift away from traditional state-centred approaches to analyzing the causes of war and toward a greater emphasis on non-state actors. This has been partly a response to real-world trends and to dissatisfaction with the failure of structural systemic theories to explain sufficiently the dynamics of warfare. It has also facilitated studies of dyadic and societal-level explanatory variables, including enduring rivalries, long cycles, power transitions, and learning and evolution.

The study of the causes of war has also diversified to include more focus on the impact of conflict on society and individuals as well as on the economy. It is increasingly recognised that war has devastating effects on human and environmental health. This includes psychological trauma, loss of physical and emotional capacity, debilitating injuries and chronic diseases as well as a disruption of family and community life.

People who are exposed to violence and conflict are more likely to experience mental illness, which can lead to homelessness as they struggle to find work. They are also at a higher risk of suicide as they try to cope with the stress and anxiety that is associated with war.

Many scholars have criticised Clausewitz for failing to consider the psychological dimensions of war. They argue that wars are rarely a result of a desire for war amongst the general public and more often arise when leaders with a disregard for human life are placed into power.

They also claim that he fails to recognise that fighting can be one of the most rewarding and enjoyable experiences for some people. It can be seen as a test of manhood and the ability to overcome adversity. It can be a thrilling adventure, full of excitement and the prospect of glory, and it is reinforced by ritual, uniforms, flags and medals. There will always be a supply of men and women willing to fight, whether in a disciplined modern army or in a rag-tag anti-modern outfit. These soldiers are not necessarily motivated by a desire for policy, but by honour, loyalty and self-sacrifice. The cost of this is high for all those concerned, but it can be particularly costly for the poor.