Alternative spellings

• warre (obsolete)

War is a behavior pattern exhibited by many primate species including man, and also found in many ant species. The primary feature of this behavior pattern is a certain state of organized violent conflict that is engaged in between two or more separate social entities. Such a conflict is always an attempt at altering either the psychological hierarchy or the material hierarchy of domination or equality between two or more groups. In all cases, at least one participant (group) in the conflict perceives the need to either psychologically or materially dominate the other participant. The perceived need for domination often arises from the belief that an essential ideology or resource is somehow either so incompatible or so scarce as to threaten the fundamental existence of the one group experiencing the need to dominate the other group. Leaders will sometimes enter into a war under the pretext that their actions are primarily defensive, however when viewed objectively, their actions may more closely resemble a form of unprovoked, unwarranted, or disproportionate aggression.

In all wars, the group(s) experiencing the need to dominate other group(s) are unable and unwilling to accept or permit the possibility of a relationship of fundamental equality to exist between the groups who have opted for group violence (war). The aspect of domination that is a precipitating factor in all wars, i.e. one group wishing to dominate another, is also often a precipitating factor in individual one-on-one violence outside of the context of war, i.e. one individual wishing to dominate another. For the purposes of this article, the focus of the remainder of this article will be upon the phenomenon of war as it is found in human society.

In 2003, Nobel Laureate Richard E. Smalley identified war as the sixth (of ten) biggest problems facing the society of mankind for the next fifty years. In the 1832 book "On War", by Prussian military general and theoretician Carl Von Clausewitz, the author refers to war as the "continuation of political intercourse, carried on with other means." War is an interaction in which two or more opposing forces have a “struggle of wills”. The term is also used as a metaphor for non-military conflict, such as in the example of Class war.

War is not necessarily considered to be the same as military occupation, murder, or genocide because of the reciprocal nature of the violent struggle, and the organized nature of the units involved.

A civil war is a war between factions of citizens of one country (such as in the English Civil War), or else a dispute between two nations that were created out of one formerly-united country. A proxy war is a war that results when two powers use third parties as substitutes for fighting each other directly.

War is also a cultural entity, and its practice is not linked to any single type of political organization or society. Rather, as discussed by John Keegan in his History Of Warfare, war is a universal phenomenon whose form and scope is defined by the society that wages it. The conduct of war extends along a continuum, from the almost universal tribal warfare that began well before recorded human history, to wars between city states, nations, or empires.

In the organised military sense, a group of combatants and their support is called an army on land, a navy at sea, and an air force in the air. Wars may be conducted simultaneously in one or more different theatres. Within each theatre, there may be one or more consecutive military campaigns. A military campaign includes not only fighting but also intelligence, troop movements, supplies, propaganda, and other components. A period of continuous intense conflict is traditionally called a battle, although this terminology is not always applied to conflicts involving aircraft, missiles or bombs alone, in the absence of ground troops or naval forces. Also many other actions may be undertaken by military forces during a war, this could include weapons research, prison internment, assassination, occupation, and in some cases genocide may occur.

As the strategic and tactical aspects of warfare are always changing, theories and doctrines relating to warfare are often reformulated before, during, and after every major war. Carl Von Clausewitz said, 'Every age had its own kind of war, its own limiting conditions, and its own peculiar preconceptions.'.

War is a conflict involving the organized use of weapons and physical force by states or other large-scale groups. Warring parties usually hold territory, which they can win or lose; and each has a leading person or organization which can surrender, or collapse, thus ending the war. Wars are usually a series of campaigns between two opposing sides involving a dispute over sovereignty, territory, resources, religion, or ideology. A war to liberate an occupied country is called a "war of liberation"; a war between internal factions within a state is a civil war. Until the end of World War II, participants usually issued formal declarations of war.