War is an organized and often prolonged conflict that is carried out by states or non-state actors.
It is generally characterised by extreme violence, social disruption, and economic destruction.
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 or intervention.
The set of techniques used by a group to carry out war is known as warfare.
An absence of war is usually called peace.
In 2003, Nobel Laureate Richard E.
Smalley identified war as the sixth (of ten) biggest problem facing humanity 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 nature, 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 deadliest war in history, in terms of the cumulative number of deaths since its start, is the Second World War, with 60-85 million deaths.
Proportionally speaking, the most destructive war in modern history has been claimed to be the War of the Triple Alliance, which took the lives of over 60% of Paraguay's population.