There are two main schools of contemporary theories about the causes of war: those based on man’s innate biological and psychological drives; and those attributed to social relations and institutions. The first school is led by ethologists, who draw analogies from animal behavior; and also by psychologists and psychoanalysts, who examine the emotional roots of societal tensions. The second school focuses on the political structures and processes that conduct war.

Throughout the history of the world, armed conflict has been conducted by political structures — states and other state actors — rather than by non-state actors. This has been true in dynastic realms, empires and global empires alike.

The nature of the State is still a key defining feature of war, even as other forms of governance arise, such as terrorism and insurrection. This defining feature has come to be the focus of attention by both optimists and pessimists as a means of assessing the preventability of future wars.

When a War begins, the state that is the target of attack must decide what to do with its military forces and equipment. This decision, however, is not always immediate. Sometimes the state must delay its initiation for a while to reorganise its military apparatus and retrain its civilian population, before it can begin to wage war.

This is not to say that a military force can’t be brought into action at once. On the contrary, in a great War, it may be done in a very short time. It is a matter of judgment as to what, in the present circumstances, can be done with all the means at a given moment, without excessive waste of energy or without conflicting with other principles of statecraft.

The difference between defence and attack enables this judgment to be made in a manner which is not possible to make in the case of a War of absolute extremes; i.e., a War which, by the law of force, should be exercised to the utmost. In this kind of War, the power of resistance depends on the fact that it is not concentrated in an instantaneous and undiluted way; but that, through the co-operation of allies, extreme tendencies are absorbed in a proportionate manner. The effect is to lessen the strength of those motives for attacking that have already been accumulated.

In addition to the power of resisting, War is a matter of coping with the effects of violence on the human body and mind, which is why the effects of a war are so long lasting and difficult to treat. As a result, many people die in a war; and those who do survive often experience severe physical and mental problems that affect their ability to function.

Moreover, the consequences of a war can be devastating to an entire society and can cause massive economic losses for decades or longer, leaving communities poor and vulnerable. This is particularly true in societies that are developing and growing, such as Africa and parts of Asia.