the american family violence researcher murray a. straus believes that disciplinary spanking forms "the most prevalent and important form of violence in american families", whose effects contribute to several major societal problems, including later domestic violence and crime. psychology the causes of violent behavior in people are often a topic of research in psychology. neurobiologist jan vodka emphasizes that, for those purposes, "violent behavior is defined as overt and intentional physically aggressive behavior against another person." based on the idea of human nature, scientists do agree violence is inherent in humans. among prehistoric humans, there is archaeological evidence for both contentions of violence and peacefulness as primary characteristics. since violence is a matter of perception as well as a measurable phenomenon, psychologists have found variability in whether people perceive certain physical acts as "violent". for example, in a state where execution is a legalized punishment we do not typically perceive the executioner as "violent", though we may talk, in a more metaphorical way, of the state acting violently. likewise, understandings of violence are linked to a perceived aggressor-victim relationship: hence psychologists have shown that people may not recognise defensive use of force as violent, even in cases where the amount of force used is significantly greater than in the original aggression. the concept of violence normalization is known as socially sanctioned, or structural violence and is a topic of increasing interest to researchers trying to understand violent behavior. it has been discussed at length by researchers in sociology, medical anthropology, psychology, psychiatry, philosophy, and bioarchaeology. evolutionary psychology offers several explanations for human violence in various contexts, such as sexual jealousy in humans, child abuse, and homicide. goetz (2010) argues that humans are similar to most mammal species and use violence in specific situations. he writes that "buss and shackelford (1997a) proposed seven adaptive problems our ancestors recurrently faced that might have been solved by aggression: co-opting the resources of others, defending against attack, inflicting costs on same-sex rivals, negotiating status and hierarchies, deterring rivals from future aggression, deterring mate from infidelity, and reducing resources expended on genetically unrelated children." goetz writes that most homicides seem to start from relatively trivial disputes between unrelated men who then escalate to violence and death. he argues that such conflicts occur when there is a status dispute between men of relatively similar status. if there is a great initial status difference, then the lower status individual usually offers no challenge and if challenged the higher status individual usually ignores the lower status individual. at the same an environment of great inequalities between people may cause those at the bottom to use more violence in attempts to gain status. media research into the media and violence examines whether links between consuming media violence and subsequent aggressive and violent behaviour exists. although some scholars had claimed media violence may increase aggression, this view is coming increasingly in doubt both in the scholarly community and was rejected by the us supreme court in the brown v ema case, as well as in a review of video game violence by the australian government (2010) which concluded evidence for harmful effects were inconclusive at best and the rhetoric of some scholars was not matched by good data. prevention the threat and enforcement of physical punishment has been a tried and tested method of preventing some violence since civilisation began. it is used in various degrees in most countries. public awareness campaigns cities and counties throughout the united states organize "violence prevention months" where the mayor, by proclamation, or the county, by a resolution, encourage the private, community and public sectors to engage in activities that raise awareness that violence is not acceptable through art, music, lectures and events. for example, violence prevention month coordinator, karen earle lile in contra costa county, california created a wall of life, where children drew pictures that were put up in the walls of banks and public spaces, displaying a child's view of violence they had witnessed and how it affected them, in an effort to draw attention to how violence affects the community, not just the people involved. interpersonal violence a review of scientific literature by the world health organization on the effectiveness of strategies to prevent interpersonal violence identified the seven strategies below as being supported by either strong or emerging evidence for effectiveness. these strategies target risk factors at all four levels of the ecological model. child–caregiver relationships among the most effective such programmes to prevent child maltreatment and reduce childhood aggression are the nurse family partnership home-visiting programme and the triple p (parenting program). there is also emerging evidence that these programmes reduce convictions and violent acts in adolescence and early adulthood, and probably help decrease intimate partner violence and self-directed violence in later life. life skills in youth evidence shows that the life skills acquired in social development programmes can reduce involvement in violence, improve social skills, boost educational achievement and improve job prospects. life skills refer to social, emotional, and behavioural competencies which help children and adolescents effectively deal with the challenges of everyday life. gender equality evaluation studies are beginning to support community interventions that aim to prevent violence against women by promoting gender equality. for instance, evidence suggests that programmes that combine microfinance with gender equity training can reduce intimate partner violence. school-based programmes such as safe dates programme in the united states of america and the youth relationship project in canada have been found to be effective for reducing dating violence. cultural norms rules or expectations of behaviour – norms – within a cultural or social group can encourage violence. interventions that challenge cultural and social norms supportive of violence can prevent acts of violence and have been widely used, but the evidence base for their effectiveness is currently weak. the effectiveness of interventions addressing dating violence and sexual abuse among teenagers and young adults by challenging social and cultural norms related to gender is supported by some evidence. support programmes interventions to identify victims of interpersonal violence and provide effective care and support are critical for protecting health and breaking cycles of violence from one generation to the next. examples for which evidence of effectiveness is emerging includes: screening tools to identify victims of intimate partner violence and refer them to appropriate services; psychosocial interventions—such as trauma-focused cognitive behavioural therapy—to reduce mental health problems associated with violence, including post-traumatic stress disorder; and protection orders, which prohibit a perpetrator from contacting the victim, to reduce repeat victimization among victims of intimate partner violence. collective violence not surprisingly, scientific evidence about the effectiveness of interventions to prevent collective violence is lacking. however, policies that facilitate reductions in poverty, that make decision-making more accountable, that reduce inequalities between groups, as well as policies that reduce access to biological, chemical, nuclear and other weapons have been recommended. when planning responses to violent conflicts, recommended approaches include assessing at an early stage who is most vulnerable and what their needs are, co-ordination of activities between various players and working towards global, national and local capabilities so as to deliver effective health services during the various stages of an emergency. criminal justice a sign that calls to stop violence one of the main functions of law is to regulate violence. sociologist max weber stated that the state claims the monopoly of the legitimate use of force practised within the confines of a specific territory. law enforcement is the main means of regulating nonmilitary violence in society. governments regulate the use of violence through legal systems governing individuals and political authorities, including the police and military. civil societies authorize some amount of violence, exercised through the police power, to maintain the status quo and enforce laws. however, german political theorist hannah arendt noted: "violence can be justifiable, but it never will be legitimate ... its justification loses in plausibility the farther its intended end recedes into the future. no one questions the use of violence in self-defence, because the danger is not only clear but also present, and the end justifying the means is immediate". arendt made a clear distinction between violence and power. most political theorists regarded violence as an extreme manifestation of power whereas arendt regarded the two concepts as opposites. in the 20th century in acts of democide governments may have killed more than 260 million of their own people through police brutality, execution, massacre, slave labour camps, and sometimes through intentional famine. violent acts that are not carried out by the military or police and that are not in self-defense are usually classified as crimes, although not all crimes are violent crimes. the federal bureau of investigation (fbi) classifies violence resulting in homicide into criminal homicide and justifiable homicide (e.g. self-defense). the criminal justice approach sees its main task as enforcing laws that proscribe violence and ensuring that "justice is done". the notions of individual blame, responsibility, guilt, and culpability are central to criminal justice's approach to violence and one of the criminal justice system's main tasks is to "do justice", i.e. to ensure that offenders are properly identified, that the degree of their guilt is as accurately ascertained as possible, and that they are punished appropriately. to prevent and respond to violence, the criminal justice approach relies primarily on deterrence, incarceration and the punishment and rehabilitation of perpetrators. the criminal justice approach, beyond justice and punishment, has traditionally emphasized indicated interventions, aimed at those who have already been involved in violence, either as victims or as perpetrators. one of the main reasons offenders are arrested, prosecuted, and convicted is to prevent further crimes—through deterrence (threatening potential offenders with criminal sanctions if they commit crimes), incapacitation (physically preventing offenders from committing further crimes by locking them up) and through rehabilitation (using time spent under state supervision to develop skills or change one's psychological make-up to reduce the likelihood of future offences). in recent decades in many countries in the world, the criminal justice system has taken an increasing interest in preventing violence before it occurs. for instance, much of community and problem-oriented policing aims to reduce crime and violence by altering the conditions that foster it—and not to increase the number of arrests. indeed, some police leaders have gone so far as to say the police should primarily be a crime prevention agency. juvenile justice systems—an important component of criminal justice systems—are largely based on the belief in rehabilitation and prevention. in the us, the criminal justice system has, for instance, funded school- and community-based initiatives to reduce children's access to guns and teach conflict resolution. despite this, force is used routinely against juveniles by police. in 1974, the us department of justice assumed primary responsibility for delinquency prevention programmes and created the office of juvenile justice and delinquency prevention, which has supported the "blueprints for violence prevention" programme at the university of colorado boulder. public health the public health approach is a science-driven, population-based, interdisciplinary, intersectoral approach based on the ecological model which emphasizes primary prevention. rather than focusing on individuals, the public health approach aims to provide the maximum benefit for the largest number of people, and to extend better care and safety to entire populations. the public health approach is interdisciplinary, drawing upon knowledge from many disciplines including medicine, epidemiology, sociology, psychology, criminology, education and economics. because all forms of violence are multi-faceted problems, the public health approach emphasizes a multi-sectoral response. it has been proved time and again that cooperative efforts from such diverse sectors as health, education, social welfare, and criminal justice are often necessary to solve what are usually assumed to be purely "criminal" or "medical" problems. the public health approach considers that violence, rather than being the result of any single factor, is the outcome of multiple risk factors and causes, interacting at four levels of a nested hierarchy (individual, close relationship/family, community and wider society) of the social ecological model. from a public health perspective, prevention strategies can be classified into three types: primary prevention – approaches that aim to prevent violence before it occurs. secondary prevention – approaches that focus on the more immediate responses to violence, such as pre-hospital care, emergency services or treatment for sexually transmitted infections following a rape. tertiary prevention – approaches that focus on long-term care in the wake of violence,