Ethnic violence is a form of political violence expressly motivated by ethnic hatred and ethnic conflict. Forms of ethnic violence which can be argued to have the character of terrorism may be known as ethnic terrorism or ethnically-motivated terrorism. "Racist terrorism" is a form of ethnic violence dominated by overt racism and xenophobic reactionism.
Ethnic violence in an organized, sustained form is known as ethnic conflict or warfare (race war), in contrast to class conflict, where the dividing line is social class rather than ethnic background.
Care must be taken to distinguish ethnic violence, which is violence motivated by an ethnic division, from violence that just happens to break out between groups of different ethnicity motivated by other factors (political or ideological).
Violent ethnic rivalry is the subject matter of Jewish sociologist Ludwig Gumplowicz's Der Rassenkampf ("Struggle of the Races", 1909); and more recently of Amy Chua's notable study, World On Fire: How Exporting Free Market Democracy Breeds Ethnic Hatred and Global Instability. Some academics would place all "nationalist-based violence" under ethnic violence, which would include the World Wars and all major conflicts between industrialised nations during the 19th century.[dubious ]
There are a variety of potential causes for ethnic violence. Research by the New England Complex Systems Institute (NESCI) has shown that violence results when ethnic groups are partially mixed: neither clearly separated enough to reduce contact nor thoroughly mixed enough to build common bonds. According to Dr. May Lim, a researcher affiliated with NECSI, "Violence normally occurs when a group is large enough to impose cultural norms on public spaces, but not large enough to prevent those norms from being broken. Usually this occurs in places where boundaries between ethnic or cultural groups are unclear."
This theory also states that the minimum requirement for ethnic tensions to result in ethnic violence on a systemic level is a heterogeneous society and the lack of a power to prevent them from fighting. In the ethnic conflicts that erupted after the end of the Cold War, this lack of outer controls is seen as the cause; Since there was no longer a strong centralized power (in the form of the USSR) to control the various ethnic groups, they then had to provide defense for themselves. This implies that once ethnicity is established, there needs to be strong distinctions, otherwise violence is inevitable.
Another theory supports that a general feeling of lack of security can cause ethnic violence, when paired with proximity to other ethnic groups. This can eventually lead to distrust of the other ethnic groups, which leads to an unwillingness to peacefully coexist with the other ethnic groups.
The emotions that tend to cause ethnic tensions, which can lead to ethnic violence, are fear, hate, resentment, and rage. Individual identities might change throughout the years, but strong emotional issues can lead to a desire to fulfill those needs above all other concerns. This strong desire to satisfy individual needs, without harming your own group, can have violent results.
Assuming that ethnic groups can be defined as a group of people who band together to protect material goods, while satisfying the need to feel a part of a group, violence resulting from ethnicity can be a result of a violation of either of these. However, this also requires that there was no peaceful solution.
Another theory states that ethnic violence is the result of past tensions. Referring to the other ethnic group based solely on their previous offences tends to increase the probability of future violence. This is referenced in the literature on ethnic violence that tends to focus on areas that have already had a history of ethnic violence, instead of comparing them with areas that have had peaceful ethnic relations.
Ethnic violence obviously does not exist in exactly the same conditions in every example. Where one case of ethnic violence might result in a drawn out genocide, another might result in a race riot. Different issues lead to different levels of intensity of violence. The problem mainly comes down to issues of group security. In situations where offensive and defensive actions are indistinguishable to outsiders, and the offensive actions are more effective in insuring group survival, then violence is sure to be present and harsh. This view of ethnic violence placed risk in areas where members of ethnic groups feel insecure about their future, not as a result of emotional tensions.
Ethnic violence often occurs as a result of individual domestic disputes spiralling out of control to large-scale conflicts. When individual disputes occur between two members of different ethnic groups, they can either result in peace or result in further violence. Peace is more likely when the offended person feels their offender will be punished sufficiently in their own ethnic group. Or peace is achieved simply through the fear of greater ethnic violence. If either the belief of retribution or the fear of violence is not present, then ethnic violence may occur.
Ethnic violence being particularly violent, there are numerous theories for preventing it, or once it starts, for ending it. Yaneer Bar-Yam of the New England Complex Systems Institute suggests that either "clear boundaries" or "thorough mixing" can reduce violence, citing Switzerland as an example.
Unfortunately, poorly planned separations do not lead to peace among ethnic groups. Religious separation between India and Pakistan left large heterogeneous areas in India where violence has since occurred.
The United States is often presented as the classic "melting pot" of ethnicities. "Ethnic" tensions in the United States are more typically viewed in terms of race.
Using the media to change perceptions of ethnicity might lead to a change in probability of ethnic violence. The use of media that results in ethnic violence is usually a cyclical relationship; one group increases messages of group cohesion in response to a perceived threat, and a neighboring group responds with messages of their own group cohesion. Of course, this only happens when outside groups are already perceived as being potential threats. Using this logic, ethnic violence might be prevented by decreasing messages of group cohesion, while increasing messages of safety and solidarity with members of other ethnic groups.
Outside forces may also be effective in decreasing the likelihood of ethnic violence. However, not all interferences from outside forces may be helpful. If not handled delicately, the possibility might increase. Outside groups can help stabilize danger zones by imposing gentle economic sanctions, develop more representative political institutions that would allow for minority voices to be heard, and encourage the respect of ethnically diverse communities and minorities. However, if done incorrectly, outside interference can cause a nationalistic lash-back.
The "Ancient Hatreds type of ethnic violence associates modern ethnic conflicts with ancient (or even mythical) conflicts. the ethnic cleansing perpetrated by Serbs in the 1990s was seen as revenge for the rule of the Croatian Ustashe, and the massacres of Bosnian Muslims was inflamed by deeply rooted hatred of the Ottoman Empire 
Further information: Ethnic conflict
Ethnic cleansing and genocide qualifies as "ethnic violence" (of the most extreme sort), because the victims of a genocide are by definition killed only based on their membership in a given ethnic group.
Other examples of ethnic violence include:
Some of the world's ongoing conflicts are, however, fought along religious rather than ethnic lines; an example of this is the Somali Civil War. The Guatemalan Civil War was fought along ideological lines (leftist rebel groups) but acquired ethnic characteristics because the rebels were primarily supported by the indigenous Mayan groups.
Terrorism against Copts in Egypt qualifies as both ethnic and religious and isn't fought in an ongoing conflict but reflects a history of sporadic and continuous attacks, over the years.