It is assumed that violence is functional at both individual and societal levels. A model developed for violent individuals is compared with a proposed model for interstate wars. In both domains, the data are consistent with the assumption that violence is functional. At the societal level, the contingencies of training are provided by official staff and require reasonably well-socialized soldiers. At the individual level, reinforcers are provided by victims, and aggressors are usually socially incompetent. In the societal model, decision makers receive reinforcers for initiating and winning wars. The combat soldiers’ behavior is somewhat paradoxical. Soldiers are thought to remain in harm’s way out of love for their buddies. The actual reinforcers for their combat behavior are unknown.