Aggression and violence remain a central clinical, public health and safety issue worldwide. Aggression has many meanings, and the term occurs in a variety of contexts. In this article, violence and aggression will be considered together. Aggression is any behavior, including verbal events, which involves attacking another person, animal, or object with the intent of harming the target. Similarly, violence is intentionally using physical force to hurt, damage, or kill someone or something.
Biological, psychological, and socioeconomic influences must be considered when discussing the etiology of aggression. Biological causes include genetics, medical and psychiatric diseases, neurotransmitters, hormones, substances of abuse, and medications. Psychological causes include numerous Diagnostic and Statistical Manual of Mental Disorders (DSM–5) diagnoses. These include bipolar affective disorder, schizophrenia, major depression, general anxiety disorder, and antisocial personality . Socioeconomic causes include interpersonal, social, group, neighborhood, economic, and cultural conditions that can create the potential for or actual violence. Importantly, these factors often act concomitantly.
Violence is ubiquitous. United States statistics, collected by the Federal Bureau of Investigation and reported in the 2013 Unified Crime Report, noted that there were an estimated 1,163,146 violent crimes that occurred nationwide. Also, information collected regarding types of weapons in violent crime showed that firearms were used in 69% of murders, 40% of robberies, and 21.6% of aggravated assaults. Furthermore, a woman was beaten every 9 seconds. On average, nearly 20 people per minute were physically abused by an intimate partner. During one year, this equates to more than 12 million women and men. Also, one in five women and one in 71 men in the United States have been raped in their lifetime. Nearly half of female (46.7%) and male (44.9%) victims of rape knew their attackers. Finally, 1 in 15 children are exposed to intimate partner violence each year, and 90% of these children are eyewitnesses to this violence.
There are greater than 16,000 homicides and 1.6 million nonfatal assault injuries requiring treatment in emergency departments every year.  The homicide rate in the US is 7.5 times higher than the homicide rate in the other high-income countries combined, largely attributable to a firearm homicide rate that was about 25 times higher.
Although the definition of aggression is simple and straightforward, its origins remain complex and frequently depend upon other, often contradictory, factors. In this exploration, there will be a review of the biological, psychological, and social causes of violence. In exploring the biological basis, there is an analysis of the genetics, brain structures, medical diseases, neurotransmitters, hormones, abused substances, and medications that contribute to aggression. In the psychological assessment, there is an investigation of the DSM–5 diagnoses linked to aggression. Finally, there is an investigation into the social and environmental roots of violence.
Although any individual may become aggressive for a variety of reasons, there is a number of specific DSM-5 diagnoses that have violent behavior as one of their features. These include bipolar affective disorder, schizophrenia, the dementia group, post-traumatic stress disorder (PTSD), and acute stress disorder. Also, several of the disorders associated with childhood and adolescence, intellectual deficiencies, some personality disorders, and intermittent explosive disorder are associated with violent behavior. As noted earlier, aggression can result from a combination of several conditions. For example, certain persons with PTSD may become violent after consuming alcohol.
It has known patients with bipolar affective disorder to become excessively agitated and aggressive, especially during the manic phase. Grandiose delusions often not only dramatically inflate their self-view but also make them demanding of others and combative to those not acknowledging their perceived greatness. Patients with schizophrenia can be aggressive when responding to command hallucinations ordering them to harm others. Patients with a wide range of dementia, such as Alzheimer disease, not only have memory deficiencies but also lose their executive functions. These executive functions provide good judgment and inhibit unacceptable impulses. This can account for some of the violence seen in long-term care facilities and in places where patients with traumatic brain injuries are treated.
Overwhelming stress can make certain individuals aggressive. It is their way of coping. Patients with PTSD struggle with a host of symptoms that can promote potential aggression. These symptoms include hypervigilance, flashbacks, and nightmares, and can lead to aggression. Several childhood diagnoses, including conduct disorder and attention-deficit/hyperactivity disorder (ADHD), can result in aggressive behavior, as can disorders along the autism spectrum, because of communication difficulties, impulsiveness, low tolerance, and frustration.
Persons with intellectual deficiencies, when confronting difficult tasks and situations, may resort to violence as a coping mechanism. ( Davies, 2016) Certain personality disorders, such as antisocial personality and borderline personality, can cause individuals to exhibit belligerence. Individuals who are antisocial lack an empathic view and have an egocentric center of gravity, which can promote aggression. A person with a borderline personality who is overwhelmed and has boundary issues can become aggressive. Finally, aggression is at the core of persons with intermittent explosive disorder.
Aside from these formal diagnoses, when people are afraid, overwhelmed, feel threatened, or feel out of control, perplexed, disorientated, or frustrated, they often respond aggressively.
Sociocultural Economic Factors
The environment can contribute to aggression on many levels: interpersonal, social, group, neighborhood, economic, and cultural conditions can create the potential for or actual violence.
Interpersonal: Interpersonal aggression occurs in a variety of settings. One of the most noted is domestic violence.  An intimate relationship can promote violence through jealousy, fear of abandonment, domination, and control issues. This involves spousal or companion abuse.  Its extreme form, intimate aggression can ultimately result in homicide or suicide. (Murphy, 2016) Other forms of domestic violence include child abuse and senior abuse. Relationships generate intense emotions. Geriatric units and long term care facilities produce intense interpersonal feelings. . Also, violence can erupt on psychiatric in-patient units.  Prisons and jails represent places where violence erupts. Bullying in any setting is both aggressive in and of itself and can lead to violence. 
Social: In social situations, frustrations can accumulate over time. This is known as an incubation period. In sociology, there is the term "relative deprivation." In this phenomenon, an oppressed group is granted some gains. They have not achieved all they wanted, but there have been some advances. However, instead of the people being grateful, they realize that they have not received all the items of which they have been deprived and act aggressively. For some, they accumulate enough things that annoy them, and they reach a "tipping" point, where the aggression frequently erupts in violence.
Group: Group experiences also can cause aggression. When many people assemble in one place, there can be growing aggression.
The treatment of aggression and violence must be based on their causes. The diagnosis leads to treatment. If a mental disorder is a responsible contributor then the specific disorder must be addressed.  Substance Use Disorders (SUD), antisocial behavior, non-adherence and recidivism are known risk factors for violence.  Therefore, these factors should be addressed in treatment and legal system.
The diagnosis and management of aggression are by an interprofessional team that may include a mental health nurse, psychiatrist, primary care and emergency providers, psychologist, pharmacist, and social worker. The treatment depends on the cause but in many cases, it may be psychiatric. Both medications and psychotherapy have been used to treat this disorder but relapses are common. Specialty care nurses including emergency room, psychiatric, and addiction will work with these patients, provide education to them and their families, and document changes for the team. Pharmacists review medications for dosage and interactions. They also participate in education. [Level 5] Many of these patients eventually run into legal problems because of their behavior.  Non psychiatric causes of aggression should be addressed by legal system. History of violence and aggression does predict future risk of violence and public health strategies could be oriented towards preventing access to firearms for individuals with a past history of violence.
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