Twenty or so years ago Cockburn published some figures that showed violent crime (or perhaps just murder) went up after every war -- and not just among veterans, but among every sector of the population. I don't remember the exact year or any exact figures, but it was impressive at the time. It was particularly impressive in reference to sectors of the population with a low murder rate: it was still low after wars but higher than before the wars.
[WS:] This is the argument developed by the UCSC criminologist Dane Archer. http://findarticles.com/p/articles/mi_m1175/is_v21/ai_4851291/pg_1
He argues that government-sponsored violence (aka war) legitimizes violence in everyday life and entices people to commit more violent acts. An interesting argument that explains (some) longitudinal variation in crime rates, but it does not explain cross-sectional variation. Crime in the US is not randomly distributed, but it concentrates in certain segments of the population, especially poor Blacks. The war effect theory does not explain that. However, it is possible to extend this argument to other factors legitimizing violence e.g. the hip hop music and gangsta rap in particular - which would make the Archer's theory better suited to explaining this kind of violence.
This would be consistent with the Wolfgang's theory of violent subculture http://www.criminology.fsu.edu/crimtheory/wolfgang.htm which in essence argues that violent norms of behavior have been internalized by the segments of the population in question (e.g. gangs as forms of social organization.)
Another possibility is the control theory of deviance proposed by Hirschi http://www.criminology.fsu.edu/crimtheory/hirschi.htm does a better job. In essence this theory attributes violence (and delinquency in general) to the breakdown of social relations in a particular social setting e.g. housing projects.
Those theories are not mutually exclusive. They explain two different aspects of violence: social structure that breeds it (Hirschi) and cultural factors that legitimate it (Archer, Wolfgang).
Wojtek