War crimes are serious violations of the laws applicable in armed conflict (also known as international humanitarian law) giving rise to individual criminal responsibility. Examples of such conduct include "murder, the ill-treatment or deportation of civilian residents of an occupied territory to slave labor camps", "the murder or ill-treatment of prisoners of war", the killing of prisoners, "the wanton destruction of cities, towns and villages, and any devastation not justified by military, or civilian necessity".

Similar concepts, such as perfidy, have existed for many centuries as customs between civilized countries, but these customs were first codified as international law in the Hague Conventions of 1899 and 1907. The modern concept of a war crime was further developed under the auspices of the Nuremberg Trials based on the definition in the London Charter that was published on August 8, 1945. (Also see Nuremberg Principles.) Along with war crimes the charter also defined crimes against peace and crimes against humanity, which are often committed during wars and in concert with war crimes.

War is an organized, armed, and often a prolonged conflict that is carried on between states, nations, or other parties typified by extreme aggression, social disruption, and usually high mortality. War should be understood as an actual, intentional and widespread armed conflict between political communities, and therefore is defined as a form of political violence. The set of techniques used by a group to carry out war is known as warfare. An absence of war (and other violence) is usually called peace.

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 treatise On War, Prussian military general and theoretician Carl von Clausewitz defined war as follows: "War is thus an act of force to compel our enemy to do our will."

While some scholars see warfare as an inescapable and integral aspect of human culture, others argue that it is only inevitable under certain socio-cultural or ecological circumstances. Some scholars argue that the practice of war 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. Another argument suggests that since there are human societies in which warfare does not exist, humans may not be naturally disposed for warfare, which emerges under particular circumstances. The ever changing technologies and potentials of war extend along a historical continuum. At the one end lies the endemic warfare of the Paleolithic^{[citation needed]} with its stones and clubs, and the naturally limited loss of life associated with the use of such weapons. Found at the other end of this continuum is nuclear warfare, along with the recently developed possible outcome of its use, namely the potential risk of the complete extinction of the human species.

Crime is the breach of rules or laws for which some governing authority (via mechanisms such as legal systems) can ultimately prescribe a conviction. Crimes may also result in cautions, rehabilitation or be unenforced. Individual human societies may each define crime and crimes differently, in different localities (state, local, international), at different time stages of the so-called "crime", from planning, disclosure, supposedly intended, supposedly prepared, incomplete, complete or future proclaimed after the "crime".^{[citation needed]}

While every crime violates the law, not every violation of the law counts as a crime; for example: breaches of contract and of other civil law may rank as "offences" or as "infractions". Modern societies generally regard crimes as offences against the public or the state, as distinguished from torts (wrongs against private parties that can give rise to a civil cause of action).

When informal relationships and sanctions prove insufficient to establish and maintain a desired social order, a government or a state may impose more formalized or stricter systems of social control. With institutional and legal machinery at their disposal, agents of the State can compel populations to conform to codes and can opt to punish or attempt to reform those who do not conform.