War is an enormously destructive phenomenon. It results in great loss of life, often destroying the social fabric of societies, and causes long term physical and psychological damage to those who survive. It can also deprive a country of resources, and cause economic/social decline. It is also a major cause of poverty, malnutrition and disease, and can even lead to economic collapse, as it can cause a decrease in production.

Despite the prevalence of non-state violence in many parts of the world, the vast majority of conflicts still involve the organised and systematic military force of states. This can be achieved through proxies, informal groups of fighters or highly organised state forces. It can be motivated by a range of reasons including the acquisition of critical natural resources, a desire for prestige or power, the defence of territory and interests, and the need to neutralise threats.

Many contemporary theories of war attempt to explain its causes by examining a variety of different factors and drives. These vary from very general, largely intuitive assertions about the innate psychological nature of man to more complex analyses utilizing concepts and techniques from modern psychology.

Another approach is to focus on strategic developments and the behaviour of powerful leaders. This tries to understand how they can produce remarkable successes despite the odds being stacked against them. It recognises that they are prone to mistakes and that they do not always have the best information, but it also acknowledges that their motives are usually sound: they want to be fair in their dealings with others and that they seek to find ways of resolving disputes by compromise.

These insights also help to explain why war can happen – not as a basic impulse or inevitability, but as the errant breakdown of huge incentives for peaceful negotiation. It is the failure of fallible, biased and nationalistic leaders to weigh up the costs of open conflict against their ambitions and ideologies that has led to the many bloodsheds in recent history.

A third view focuses on the cultural and social aspects of bellicosity. These consider the role of culture in arousing, channelling and legitimising violent urges, and the process of turning them into useful, purposeful human activity that is viewed as worthy of sacrifice. It combines long-term anthropological and psychological insights with more specific cultural/social situations, which can be quite different in one culture to another.