War is an event that occurs when the will of nations to fight is irresistible, and the power to bring about such a conflict is insufficient to prevent it. It is not simply a phenomenon of the political world, shaped by international relations theory and practice, but of the physical world and the nature of human beings. It is a process that, to some degree, takes place in every country on earth. The experience of war shapes the way in which its participants live their lives. It changes the language people use, how they name places, and encourages a variety of social changes that are both positive and negative.

The causes of War have long been the subject of speculation, from general, often merely intuitive assertions about human nature to complex analyses that employ concepts and techniques from modern psychology. These theories are usually based on the belief that a nation’s character is determined in part by its history and its culture, and that major events such as wars influence the national psyche. Thus the idea of the “national spirit” is one of the primary underlying forces in the concept of War, as well as the sense of revenge that can be triggered by events such as assassinations and natural disasters.

Another set of explanations involves a country’s economic interests. There are those who assert that, to a great extent, the world’s wealth is limited, and that increasing the wealth of one state means the loss of wealth for others. This belief has, to some degree, shaped the course of inter-state wars. But the emergence of Adam Smith and modern economic thinking has dramatically changed this view. Wealth can now be increased by the division of labour, mechanical sources of energy, economies of scale and cooperation. This has effectively ended the motives for war that were based upon material aggrandisement.

Many thinkers have also pointed to the fact that the act of war itself is a highly unpredictable process. Aside from the initial impulse to go to war, military operations are a matter of chance, and any number of events can throw a wrench into an otherwise carefully planned operation.

There are a number of reasons why this is the case, including the tendency for humans to be over-confident about their own abilities; the difficulty of predicting what an opponent will do; and the fact that the nature of military technology changes rapidly, bringing new possibilities into play.

Despite these unpredictable elements, it is still possible to identify some continuities in the conduct of war. Observant military personnel will notice the repetition of certain types of situations, e.g., the need to gather enough material in advance to sustain a war of some years duration. These continuities are evident in the form of drills and doctrine, but they are also apparent in the way that individual military men behave in different situations. This is why a commander will impose some level of discipline on his troops even though the outcome of any particular encounter will remain uncertain.