In one sense, the London riots defy explanation. All mob violence does. When attempting to explain it, sociologists typically begin by telling you there's no way to predict what will trigger a violent uprising.

"The most important feature of collective behavior phenomena, especially riots, is that they are spontaneous and essentially unpredictable, as are so many statistically rare events," said Erich Goode, a professor emeritus of sociology at State University of New York, Stony Brook who has researched and written about deviance, criminology and collective behavior for several decades.

Like an earthquake or solar flare, the sudden escalation of violence following an accidental police shooting that occurred Aug. 4 in London was somewhat random.

That said, it is possible to analyze the psychology behind the crowd violence that followed. The most widely accepted theory to explain such events was put forth by psychologist Clifford Stott at the University of Liverpool in England to explain football hooliganism. "Of central importance is that we know that 'riots' cannot be understood as an explosion of 'mob irrationality,'" Stott explained in the British newspaper The Independent. "Nor can they be adequately explained in terms of individuals predisposed to criminality by nature of their pathological disposition."

Contrary to the belief that mobs act solely as a single-minded ball of chaos, Stott's theory of crowd behavior, called the Elaborated Social Identity Model, holds that individuals in a crowd do keep thinking for themselves. On top of their individual identities, though, they also develop a makeshift social identity, which includes everyone else in the group. When the group faces opposition, such as police indiscriminately bashing its members with batons, the social identity congeals. Members of the group begin to work together to fight what it sees as its common oppressors.

This best explains the escalation of violence in the aftermath of the police shooting: Members of the mob felt threatened and reacted violently to preserve themselves. [The Psychology of Fear]

Police response

To prevent solidifying a social identity among rioters, Stott advises police to maintain the perception that they're acting legitimately when dealing with a crowd. They must do this by targeting criminal behavior specifically, rather than treating everyone in the crowd as equally criminal. Stott believes, and research seems to support this notion, that crowds respond to rational police action by behaving rationally themselves.

Gary Marx, a sociology professor emeritus at MIT and the author of several books on collective behavior and uprisings, also views the police response to crowds as the determining factor in how events will progress. "Authority often either overresponds or underresponds," Marx told Life's Little Mysteries, a sister site to LiveScience. "If they respond too quickly or too severely, it can provoke a reaction, but if they're too slow, people think they can get away with more."

Indiscriminate responses such as the use of tear gas can be especially dangerous, as they can be perceived as unfair, he said. Through social media, word quickly spreads of unreasonable police brutality. "Clearly the new means of communication are a game-changer," Marx said.

Mixed motives

In the case of the London riot, which has since spread to other parts of England, the Metropolitan Police may have lost their legitimacy from the outset when they shot Mark Duggan, a drug dealer who they mistakenly thought was shooting at them.

Those protesters who felt themselves to be in the same group as Duggan were quick to rise to violence. However, strangely, the members of that group don't fit any specific category.

"The thing that's so distinctive about the London riots … and different from past riots that behavioral scientists have written about, is that the convergence of rioters now is of heterogeneous actors, with different motives: some acting on political motives, others to loot, still others to engage in wild and crazy behavior," Goode wrote in an email. "So it's difficult to theorize about similar behavior … that is caused by very different impulses."

Simon Moore, a researcher with the Violence & Society Research Group at Cardiff University in Wales, thinks there's one factor that may be uniting all the rioters: The perception that they have low status. In research he conducted last year with colleagues at the University of Warwick, Moore found that low economic rank — being poorer than others in the same geographic region — rather than actual poverty, which is defined as not being able to afford things you need, elicits misery.

Along with misery, a fair amount of research has found that low status also leads to feelings of animosity, Moore said. "[Yet] another area of work suggests low status elicits stress, and this is implicated in aggression," he wrote in an email. [Is Rage a Mental Disorder?]

Martin Luther King Jr. had a similar take on the psychology of the disenfranchised: "There is nothing more dangerous than to build a society with a large segment of people in that society who feel that they have no stake in it; who feel that they have nothing to lose. People who have a stake in their society, protect that society, but when they don't have it, they unconsciously want to destroy it."

This article was provided by Life's Little Mysteries, a sister site to LiveScience. Follow us on Twitter @llmysteries, then join us on Facebook.