Recently, there have been a number of high profile cases of institutional aggression; notably, the atrocities that were committed by American soldiers at the Abu Ghraib detention centre and by British soldiers in Baha Mousa.

Social Psychologists have attempted to explain institutional aggression by identifying the social forces that influence this type of aggressive behaviour. In The Lucifer Effect, Philip Zimbardo (2007), for example, explains the atrocities in Abu Ghraib in terms of seven well known social psychological processes

Zimbardo's Seven Social Processes That Grease the Slippery Slope of Evil

1. Mindlessly taking the first small step
2. Dehumanisation of others
3. Deindividuation of self (anonymity)
4. Diffusion of personal responsibility
5. Blind obedience to authority
6. Uncritical conformity to group norms
7. Passive tolerance of evil through inaction or indifference

Mindlessly taking the first small step

Atrocious acts rarely occur suddenly; usually, they begin small (perhaps a prisoner is hit or slapped) and escalate gradually into more terrible abuse.  According to Zimbardo, who acted as an expert witness in the Abu Ghraib trials, the abuse that took place in the detention centre began innocuously and became a routine part of the night shift before it escalated into horrific torture. This process is analogous to the 'gradual commitment' shown by participants in the Milgram experiments: the participants did not feel particularly bad about giving the 'learner' a 15 volt shock and each subsequent shock was an increase of only 15 volts, which made it easy for participants to build up to a shock level of 450 volts; one wonders how many participants would have obeyed the experimenter if the first shock had been 450 volts.

Dehumanisation of others

Dehumanisation occurs when members of an outgroup are considered to be less than human; an example of this is considering the other group members as being like animals. Thinking of other people in this way makes it easier to treat them badly. There are many examples of dehumanisation in warfare: American GIs in Vietnam and Korea called the native population "Gooks"; US snipers who killed women and children in Falluja in Iraq boasted of "killing rats in their nests"; Prince Harry, while working as a soldier in the Middle East said that one of his Asian colleagues looked "like a raghead", a term that is in common parlance in the British Army when refering to Arabs; The famous Zimbardo Prison Simulation study began with the prisoners being stripped and disinfected by the guards, creating the impression that they were dirty and sub-human; in Abu Ghraib, US soldiers rode on the backs of naked prisoners, treating them them “like donkeys”; General Ricardo Sanchez claimed that prisoners at Abu Ghraib and Guantanamo Bay were “like dogs”.

Deindividuation of self (anonymity)

Deindividuation occurs when a person becomes less identifiable and, thus less self-conscious. Research has consistently shown that when people are deindividuated they are more likely to act in an aggressive or antisocial manner; for example, Zimbardo (1969) found that participants who wore hoods and lab coats gave electric shocks for a greater duration than those wearing their normal clothes. However, not all research has supported the idea that deindividuation leads to more antisocial behaviour; Johnson and Downing (1979) found that while Ku Klux Klan style hoods and robes did lead to more aggressive behaviour, nurses uniforms resulted in less aggressive shocks.

Some researchers have argued that deindividuation causes people to adhere more to group norms (Postmes and Spears, 1998). The implication of this for institutions is that deindividuation through uniforms is likely to lead to greater conformity to whatever the established norms are; so if atrocious behaviour becomes the norm it is more likely to be imitated.

Diffusion of personal responsibility

Diffusion of responsibility occurs when a number of bystanders are observing a negative event where some sort of intervention is required, usually at a cost to the intervener. The more bystanders that are present, the less likely that one of them will intervene, as they all assume that someone else will take responsibility. In cases such as Abu Ghraib there is a high cost to the whistle blower: Joe Darby who handed the photos of the abuse at Abu Ghraib to authorities, was not hailed as a hero when Donald Rumsfeld revealed his identity on television; he lived in fear of his life, his family was driven out of their home and he was called a traitor by many in the town where he grew up.

Blind obedience to authority

The series of obedience studies carried out by Stanley Milgram in the 1960s illustrated the extent to which ordinary people are willing to obey a malevolent authority figure. In the standard experiment where participants were asked to give electric shocks to another participant (really a confederate of the experimenter) in response to his incorrect answers on a memory test, 65% of participants continued to obey as the shocks increased from 15 volts through to 450 volts at 15 volt intervals. All of the participants went as far as 300 volts.

This blind obedience to authority has also been demonstrated in a real life institutional setting by Hoffling et al. (1966) where 21 out of 22 nurses obeyed a doctor’s instructions to administer a fatal dose of a (fake) drug to a patient. Thus, in situations where aggressive acts are being committed by those in positions of authority, aggression is likely to be perpetuated by those under their command.

The My Lai massacre happened because soldiers blindly obeyed an order to kill all guerrilla and North Vietnamese combatants and "suspects" (including women and children, as well as all animals), to burn the village, and pollute the wells.

Uncritical conformity to group norms

Conformity refers to the tendency of members of a group to behave in a similar way to other members of the group. This can happen because of informational social influence – one believes that other group members know more than oneself - or normative social influence – one conforms to the norms of the group because one wants to fit in and not be seen as deviant.

Army battalions are extremely cohesive social groups and are separated from civilian society for long periods of time; this means that normative social pressure is likely to be exceptionally high. Consequently, in situations such as Abu Ghraib it is unlikely that group members will dissent.

Passive tolerance of evil through inaction or indifference

The seventh of Zimbardo’s social processes that grease the slippery slope of evil is perhaps a consequence of some of the other processes: dehumanisation of the victims of aggression makes it less likely that a person will care enough to act; diffusion of personal responsibility makes inaction more likely as one believes that someone else will; and strong normative social pressure makes the cost of dissention difficult to contemplate.

Other factors

In addition to the factors above, Zimbardo proposes that people in positions of power are also responsible for institutional aggression. Institutions such as the military need to be aware that there is a high risk of atrocities taking place because of the nature of the institution: soldiers are trained to obey orders unquestioningly so that they do not question those that involve them killing the enemy or putting themselves at risk of being killed; group cohesiveness makes teamwork within battalions more effective; dehumanising the enemy makes it psychologically possible to kill and live with the fact that one has killed – if one were to consider the enemy as a human being who has joined the army to support his family, it would be more difficult. Therefore, those in positions of power have a responsibility to ensure that systems are in place to prevent institutional aggression.