Violence is "the use of physical force so as to injure, abuse, damage, or destroy." Less conventional definitions are also used, such as the World Health Organization's definition of violence as "the intentional use of physical force or power, threatened or actual, against oneself, another person, or against a group or community, which either results in or has a high likelihood of resulting in injury, death, psychological harm, maldevelopment, or deprivation."
Globally, violence resulted in the deaths of an estimated 1.28 million people in 2013 up from 1.13 million in 1990. Of the deaths in 2013, roughly 842,000 were attributed to self-harm (suicide), 405,000 to interpersonal violence, and 31,000 to collective violence (war) and legal intervention. In Africa, out of every 100,000 people, each year an estimated 60.9 die a violent death. For each single death due to violence, there are dozens of hospitalizations, hundreds of emergency department visits, and thousands of doctors' appointments. Furthermore, violence often has lifelong consequences for physical and mental health and social functioning and can slow economic and social development.
In 2013, assault by firearm was the leading cause of death due to interpersonal violence, with 180,000 such deaths estimated to have occurred. The same year, assault by sharp object resulted in roughly 114,000 deaths, with a remaining 110,000 deaths from personal violence being attributed to other causes.
Violence in many forms can be preventable. There is a strong relationship between levels of violence and modifiable factors in a country such as concentrated (regional) poverty, income and gender inequality, the harmful use of alcohol, and the absence of safe, stable, and nurturing relationships between children and parents. Strategies addressing the underlying causes of violence can be relatively effective in preventing violence, although mental and physical health and individual responses, personalities, etc. have always been decisive factors in the formation of these behaviors.
It has not yet been determined why chimpanzees, genetically the closest relative of man, under some conditions live peacefully and at other times practice murderous genocidal and cannibalistic "warfare". Chimpanzees do engage in predation of other species, and it is therefore an open question how far this kind of violence is related to their intra-specific violence; particularly since they often eat the other chimpanzees that they kill. The exact interplay of innate violent predispositions, ecology, resource competition, mate competition, predation and territoriality are not yet understood.
Although fighting occurs widely throughout animals species, only a few cases of destructive intra-species fighting between organized groups of have ever been reported among naturally living species, and none of these involve the use of tools designed to be weapons. Normal predatory feeding upon other species cannot be equated with intra-species violence. Warfare is a peculiarly human phenomenon and does not occur in other animals.