War is a violent conflict between opposing forces to achieve political objectives such as territory, control, power and revenge. It is a complex and costly enterprise, often with long-lasting consequences for the victorious and defeated. In terms of societal impact, warfare can result in widespread violence, loss of life and debilitating trauma for civilians. This is especially true of civil wars, in which armed rebels have increasingly targeted civilians as their main targets.

Emotional factors have a powerful influence on the probability of war and may overshadow more purely rational considerations. Emotional factors can include fear, honour, survival or interest in property, bellicose culture, domestic pressure or perceived injustice, reaction to incursion or ambition or opportunism. These factors may be the cause of a particular war or they may be exacerbated by the conduct of a specific war.

The causes of war have changed over time, but a core of factors remain. Economic motives for war have fallen away as mercantilism gave way to more sophisticated understandings of wealth, but security-driven wars continue to increase in frequency. These wars, despite their lower intensity than other types of warfare, are driven by the desire to maintain or assert a dominant position in global affairs.

Military historians and theorists have developed many explanations for the causes of war, ranging from a combination of ‘primordial’ ethnic passions to economic and political interests. These explanations are not always correct and can divert attention from more important underlying issues.

As with definitions of war, discussions of its etiology are often coloured by broader philosophical issues about the nature of determinism and freedom. The debate inevitably involves the question of how to distinguish wars between states from riots and rebellions, culturally evolved, ritualistic or guerrilla uprisings that appear to have no centrally controlled body.

It has been argued that the introduction of new weapon systems and techniques, such as firearms, tanks, aircraft and nuclear weapons, has changed the nature of war. But this is too simplistic a view of the phenomenon and is unsupported by the evidence.

Even when new technologies are introduced, the underlying causes of war remain unchanged. They are still a mixture of emotional, psychological and material factors that are influenced by the context and environment in which they occur. As long as there are human beings with a need to express their natural desires, there will be conflict. The most serious risks come when analysts forget this and fail to understand the complexities of the process, so that they misinterpret its causes. This would be like intensive care doctors forgetting that people are naturally healthy. Getting the causes of war wrong leads to misunderstanding, overestimation and false prevention measures that may actually make things worse. For example, the current focus on the role of drones in war is based on faulty assumptions about the cause of violence and the potential risks involved. As a result, the costs of this technology could be much higher than necessary.