Understanding violent extremism in the 21st century: the (re)emerging role of relative deprivation

Recently, the world has experienced a wave of violent protest, and in particular Islamist and right-wing extremism have become

"They are the kings, and we are the slaves. Enough." Suzy Barakat, protester, Beirut, 2019 [1] From 2017 to 2020, the world witnessed a wave of violent protests, ranging from Bolivia to Hong Kong, France, Spain, Venezuela, Iraq, Lebanon, and Chile, to name just a few. At the same time, many societies have faced challenges related to individuals and groups engaged in terrorist and other types of violent extremist activities.
Most prominent examples include the increase of rightwing extremism in the West and the rise of ISIS in the Middle East [2]. In this review, we aim to demonstrate that the experience of relative deprivation is a motive often shared by individuals and groups engaged in such contemporary forms of violent extremism. Consequently, we argue that, due to rising social inequalities and corresponding power asymmetries intra-and internationally, the experience of relative deprivation is likely to become one of the key factors driving violent extremism across groups, cultures and contexts in the 21st century.

Relative deprivation and collective action
A central way by which humans obtain information about themselves and their social standing in society is through social comparisons [3], and relative deprivation describes a negative evaluation resulting from this [4][5][6][7]. Specifically, relative deprivation involves the perception that oneself or one's group does not receive valued resources, goals, ways or standards of living, which others possess and one feels rightfully entitled to [8 ].
Relative deprivation has for long time been used to explain why people engage in political and social protest [for a review, see Ref. [6]]. Underlining its subjective nature, relative deprivation can trigger collective action even for people who are not personally and directly affected by injustice but who still perceive themselves to be victims of it [e.g. Most research so far has investigated the role of relative deprivation for normative forms of collective action. Whereas many theories and models suggest that relative deprivation also plays a key role for extremism [28,29], little research has directly investigated this relationship, and especially applications to current forms of extremism are missing. However, as we aim to demonstrate, in particular research from the recent years supports the central role of relative deprivation for understanding contemporary types of extremism among low-power and high-power groups alike.
Extremism among low-power groups: fighting against perceived injustice Extremism among high-power groups: defending or challenging the status quo The reviewed studies confirm the role of relative deprivation among groups who have low power intra-and internationally. But what about groups with relatively high power within these social systems? Generally, in an attempt to defend their dominant status, members of high-power groups seem to show more violent extremism against out-groups when intergroup inequality is high [45][46][47]. Some evidence further suggests that this tendency is potentiated by the subjective experience of relative deprivation. In a study with Dutch youth, experiences of group and personal relative deprivation were both correlated with more support for right-wing extremist violence and own violent intentions [48]. Similarly, in Indonesia where Islam is the dominant religion, the more injustice Muslim majority-group members perceived against their group, the more they supported harm against other people to enforce their religious group's political influence [49]. Causal evidence for such a relationship was further obtained in a recent experimental study [50 ]. White U.S. Americans with a Republican affiliation were asked to recall potential experiences of relative deprivation or mundane life experiences. Participants in the relative deprivation condition showed a stronger willingness to violently persecute political out-groups. Interestingly, mediation analyses showed that effects on these extremist tendencies were largely mediated by people's increased closeness [i.e. identity fusion; see Ref. 51] with their political leader. In other words, the more relative deprivation people experienced, the more they fused with their political leader, which in turn made them more willing to violently fight people who this leader had identified as threats. This finding may help explain past political movements in which extreme leaders were adored and followed, and that ultimately resulted in intergroup atrocities. Moreover, the observed processes may be particularly valuable when aiming to understand intergroup relations in times of increasing populism and political authoritarianism [also see Refs. 52,53].
However, not all members of high-power groups support or engage in efforts to violently maintain the status quo, and often the opposite is true. In these cases, relative deprivation again seems to play a decisive role. For instance, perceiving that out-groups experience injustice may under certain conditions motivate normative collective action on their behalf [9, [54][55][56]. But under which conditions are people willing to engage in non-normative, violent action to support groups they do not belong with? Recent work suggests that this is the case especially if the unjust treatment that an out-group is perceived to endure clashes directly with people's ideological convictions. For instance, in a series of studies [57], leftists were more likely to engage in violent protest for out-groups who tend to be seen as victims of oppression (e.g. Palestinians) than for out-groups for whom such a perception often is lacking (e.g. Kurds). Yet, experimental evidence showed that this tendency could be altered. Once the Kurds' situation was framed as an asymmetrical occupation rather than a symmetrical war (or a neutral control condition), leftists felt closer with the Kurdish people, which in turn was related to more extreme political protest on their behalf. Further analyses with a sample of aspiring foreign fighters corroborated these results. When Leftist foreign fighters experienced a moral obligation to support the Kurds in their struggle, they experienced more closeness to them and, subsequently, reported a higher likelihood to join the Kurdish People's Protection Units (YPG) in their fight against ISIS and to sacrifice their lives for the Kurdish people.

Conclusion
Perceptions of relative deprivation are powerful motivators for contemporary forms of violent extremism across cultures and contexts. They may explain the violent behavioral intentions of (a) low-power groups who aim to improve their life prospects and challenge the hierarchy, (b) high-power groups who aim to maintain the selfserving status quo, and (c) those helping out-groups whose life conditions are perceived as desperate. Overall, the predictive power of relative deprivation depends on how fairly resources, power and social status are distributed within social systems, and, importantly, how this distribution is perceived [18 ]. As social inequalities internationally and within many societies around the world are increasing, if relative deprivation is not a key driver of violent extremism in the 21st century yet, it can be expected to become so over the next few decades.

Conflict of interest statement
Nothing declared. 18.

CRediT authorship contribution statement
Power SA: Why a richer world will have more civic discontent: The infinity theory of social movements. Int J Qual Methods 2020. Online advance article. In this paper, the author proposes a new theory of social movements. The particularly innovative part of the theory involves its temporal dimension that often has been neglected in previous models. Specifically, it takes into account people's perception of the past and views of the future as factors influencing experiences such as relative deprivation, which ultimatelly result in collective action. A quest for significance is known for predicting violent extremism. Across diverse, hard-to-reach samples and cultures, the authors showed that this relationship is moderated by the extent to which a social context is radical. Especially the role of quest for group-based significance was potentiated within such radical social contexts. This finding is important as it emphasizes the need to combine individual and contextual perspectives when understanding violent extremism. 1069397119882364.This study tested whether relative deprivation, conceptualized as a decrease in population-level happiness over time, would predict highly-consequential, political events. Specifically, the authors found that, even when controlling for economic factors, a decrease in happiness from 2009 to 2010 prospectively predicted the extent to which countries experienced political destabilization during the Arab spring. The study is of importance as it shows how psychological changes and developments with regards to relative deprivation can predict future large-scale political events.