War is a state of armed and often prolonged conflict carried on between states, nations, or parties[1][2] typified by extreme aggression, societal disruption, and high mortality.[1] As a behavior pattern, warlike tendencies are found in many primate species,[3] including humans, and also found in many ant species.[4][5][6] The set of techniques used by a group to carry out war is known as warfare. An absence of war is ususally called peace.

War generally involves two or more organized groups or parties (often, nations). Such a conflict is always an attempt at altering either the psychological or material hierarchy of domination or equality between such groups. In all cases, at least one participant (group) in the conflict perceives the need to either psychologically or materially dominate the other participant.

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.[7]

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.[8] 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."[9] War is an interaction in which two or more opposing forces have a “struggle of wills”.[10] The term is also used as a metaphor for non-military conflict, such as class war.

War is a seemingly inescapable and integral aspect of human culture. 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.[11] The conduct of war extends along a continuum, from the almost universal primitive endemic warfare that began well before recorded human history, to advanced nuclear warfare between global alliances, with the recently developed ultimate potential for human extinction.