War is one of the most difficult of all human activities to understand. It is not just a violent fight between states and their peoples; it is also a social activity, involving complex interrelationships and interacting elements. It is a political, psychological, and philosophical phenomenon. In addition, it is often a product of technological change. For example, the invention of gunpowder and other firearms and the acceleration of technological advances have caused dramatic changes in warfare. It has also fostered a number of different theories of war and its causes.

Theories of war’s cause vary from those that concentrate upon innate drives, such as those developed by ethologists who draw analogies with animal behaviour, to those that concentrate on social relations and institutions. Those who concentrate on the latter tend to be optimists concerning the avoidability of war, whilst those who concentrate upon the former are usually pessimists.

There are many causes of war – poverty, hatreds, injustices and the possession of armaments are all commonly mentioned – but there is a great deal of dispute about whether these actually increase the probability of conflict. Moreover, when these causes are considered in isolation it is likely that they do not account for the overall incidence of warfare.

The key to understanding the causes of war lies in the fact that it is the result of a breakdown of extremely powerful incentives for peace. When those incentives break down, the motivations of opponents to negotiate a settlement or to wage war become much stronger.

This is what makes it so hard to predict when or how a war will end. There are many reasons why war occurs, but the most common reason is that there is a large wedge of political territory occupied by leaders who have very different interests. This wedge consists of a range of factors including the idiosyncratic ideologies and biases that drive the leaders, the strength of their respective military forces, their desire for power and wealth, and their ability to persuade their opponents to compromise.

The fact that these five factors converge to create the conditions for war means that it is unlikely that it can be eliminated entirely. But there are measures that can be taken to limit the damage, such as limiting the size of the army and the types of weapons used. These should be accompanied by more robust international sanctions and a willingness to prosecute those found to be responsible for war crimes. This will help to reduce the frequency and severity of war. It will also reduce the amount of resources that have to be spent on rebuilding after war has ended, thereby freeing up funds that can be directed towards other purposes. In addition, there is the need to focus more attention on mental health and the impact of war on children. This is particularly important given that the onset of war can lead to long-term effects on their cognitive and physical development.