The link between EU identification and responses to a war between non-EU countries over time.

The European Union (EU) is portrayed as a "normative power" that promotes democracy. How does identifying with the EU identity predict citizens' responses to a war between two non-EU countries, where one (Ukraine) appears as the victim (i.e., a nation suffering significant harm as a result of military aggression by another country) and the other (Russia) as the aggressor (i.e., a nation initiating military aggression against another country)? This study tested two contrasting, yet not mutually exclusive hypotheses. Based on the underlying idea that Ukraine is perceived to share similar (European) values while Russia is perceived to deviate from these values, the "humanitarian influence of the EU identity hypothesis" hypothesized that identification with the EU identity predicts increased support for the victim group (Ukraine) and condemnation of the aggressor group over time. Based on the "protective effect of EU identity hypothesis," however, a reverse temporal order was also hypothesized. We conducted a two two-wave study among Greek participants. Our findings provided full support for the first hypothesis and partial support for the second hypothesis. Identification with EU identity predicts increasingly stronger opposition to an intergroup conflict between non-EU countries.

When population growth intensifies intergroup competition, female colobus monkeys free-ride less.

Intergroup aggression often results in the production of public goods, such as a safe and stable social environment and a home range containing the resources required to survive and reproduce. We investigate temporal variation in intergroup aggression in a growing population of colobus monkeys (Colobus vellerosus) to ask a novel question: "Who stepped-up to produce these public goods when doing so became more difficult?". Both whole-group encounters and male incursions occurred more frequently as the population grew. Males and females were both more likely to participate in whole-group encounters when monopolizable food resources were available, indicating both sexes engaged in food defence. However, only females increasingly did so as the population grew, suggesting that it was females who increasingly produced the public good of home range defence as intergroup competition intensified. Females were also more active in male incursions at high population densities, suggesting they increasingly produced the public good of a safe and stable social environment. This is not to say that males were chronic free-riders when it came to maintaining public goods. Males consistently participated in the majority of intergroup interactions throughout the study period, indicating they may have lacked the capacity to invest more time and effort.

The effect of intergroup competition outcome on ingroup cooperation: insights from the male warrior hypothesis.

Introduction: The Male Warrior Hypothesis (MWH) proposes that sex-specific selective pressures have promoted male cooperation with the ingroup members to outcompete rival groups. However, intergroup conflicts do not occur in isolation and the outcomes of previous competitions may influence group cooperativeness. Since this phenomenon is not well understood, we aimed to shed light on the effect of previous competition outcome on later cooperative behavior under intergroup conflicts. Based on the MWH, we hypothesized that repeated contests between groups could enhance ingroup cooperation, regardless of the outcome of the previous contest because status is at risk, but when competition is not present, participants would move to the symmetric equilibria. Methods: To test this hypothesis, we recruited 246 individuals organized in groups of 6 and measured cooperation using a threshold public good game over two rounds, manipulating the outcome in the first round to create groups of winners and losers. Results: Our results show that intergroup conflict scenarios promoted cooperation in both victory and defeat conditions, whereas, in the control scenario only losers increased their cooperation. Discussion: We argue that winners under the presence of an external threat may enhance in-group cooperation in order to assure their status; whereas, losers may be attempting to regain it.

In-between group membership within intergroup conflicts: The case of Druze in Israel.

In-between groups encompass individuals who simultaneously belong to social categories that are often seen as mutually exclusive in addition to maintaining their distinct group identity. The current paper sheds light on how members of in-between groups manage their relations within intergroup conflicts. Three studies were conducted among the Druze minority in Israel, a group that is ethnically Arab and shares the Arab identity with the Arab-Palestinian minority in Israel and simultaneously identifies as Israeli. In Study 1 (N = 300), we found that identification as Druze was positively associated with the identification as Arab and Israeli. In Study 2, we examined Druze's endorsement of conflict narratives compared to Jewish-Israeli and Palestinian citizens (N = 271). While the latter participants endorsed their ingroup narrative more than the outgroup narrative, Druze participants endorsed both narratives equally. In Study 3, we tested Druze's solidarity with the Palestinian minority against the 2018 Nation-State Law. We found that overall, Druze participants (N = 568) endorsed more inclusive amendments that benefited the Druze and Palestinians than exclusive amendments that benefited the Druze only. In all studies, we tested the role of identification with the rival groups. We discuss these findings and suggest possible underlying mechanisms.

Between victory and peace: Unravelling the paradox of hope in intractable conflicts.

Previous research on group-based hope has predominantly focused on positive intergroup outcomes, such as peace and harmony. In this paper, we demonstrate that hope experienced towards group-centric political outcomes, such as a victory in a conflict and defeating the enemy, can be detrimental to peace. In Study 1, conducted among Israeli Jews, hope for victory over the Palestinians was uniquely associated with more support for extreme war policies, whereas hope for peace generally showed the opposite associations. In Study 2, we replicated these results among Muslim Pakistanis regarding the Pakistan-India dispute. Notably, in both Studies 1 and 2, only hope for victory significantly predicted personal violent extremist intentions. In Study 3, conducted with a representative sample of Israeli Jews, we found three latent profiles of hope: victory hopers, peace hopers, and dual hopers (hoping for both peace and victory). Finally, in preregistered Study 4, we longitudinally investigated how hopes for victory and peace changed from a relatively calm period in 2021 to the Israel-Hamas War of 2023, utilizing a Bivariate Latent Change Score analysis. Increases in hope for victory during the highly intense war explained the increase in support for violence. We discuss implications, limitations, and directions for future research.

Sadism in the context of intergroup aggression.

People more readily harm members of outgroups than ingroups, often enjoying the inflicted agony. Yet it remains unclear how these malevolent tendencies towards outgroups relate to sadism. Sadists often harm others, driven by a desire to feel pleasure from their suffering. In attempt to bridge these two lines of research, this work examined relationships between sadism and aggression against ingroup and outgroup members in three studies (total N = 755) that focused on two groups with a history of conflict (i.e., the United Kingdom and the Republic of Ireland). Across all studies, British participants' sadistic tendencies were just as strongly linked to their aggression against ingroup members (i.e., British partners) as to their aggression against outgroup members (i.e., Irish partners). Despite this lack of a preference for greater outgroup aggression, they tended to enjoy outgroup aggression more than ingroup aggression, especially at its extreme levels. These findings extend works linking sadism to aggression into the domain of intergroup relations and bind together research on sadism and intergroup schadenfreude.

Signals of belonging: emergence of signalling norms as facilitators of trust and parochial cooperation.

Mechanisms of social control reinforce norms that appear harmful or wasteful, such as mutilation practises or extensive body tattoos. We suggest such norms arise to serve as signals that distinguish between ingroup 'friends' and outgroup 'foes', facilitating parochial cooperation. Combining insights from research on signalling and parochial cooperation, we incorporate a trust game with signalling in an agent-based model to study the dynamics of signalling norm emergence in groups with conflicting interests. Our results show that costly signalling norms emerge from random acts of signalling in minority groups that benefit most from parochial cooperation. Majority groups are less likely to develop costly signalling norms. Yet, norms that prescribe sending costless group identity signals can easily emerge in groups of all sizes-albeit, at times, at the expense of minority group members. Further, the dynamics of signalling norm emergence differ across signal costs, relative group sizes, and levels of ingroup assortment. Our findings provide theoretical insights into norm evolution in contexts where groups develop identity markers in response to environmental challenges that put their interests at odds with the interests of other groups. Such contexts arise in zones of ethnic conflict or during contestations of existing power relations. This article is part of the theme issue 'Social norm change: drivers and consequences'.

The Intergroup Value Protection Model: A Theoretically Integrative and Dynamic Approach to Intergroup Conflict Escalation in Democratic Societies.

SCIENTIFIC ABSTRACT: We review social-psychological evidence for a theoretically integrative and dynamic model of intergroup conflict escalation within democratic societies. Viewing individuals as social regulators who protect their social embeddedness (e.g., in their group or in society), the intergroup value protection model (IVPM) integrates key insights and concepts from moral and group psychology (e.g., group identification, outrage, moralization, protest) into a functional intergroup value protection process. The model assumes that social regulators are continuously looking for information diagnostic of the outgroup's intentions to terminate the relationship with the ingroup, and that their specific cognitive interpretations of an outgroup's action (i.e., as a violation of ingroup or shared values) trigger this process. The visible value-protective responses of one group can trigger the other group's value-protective responses, thus dynamically increasing chances of conflict escalation. We discuss scientific implications of integrating moral and group psychology and practical challenges for managing intergroup conflict within democratic societies. PUBLIC ABSTRACT: The 2021 Capitol Hill attack exemplifies a major "trigger event" for different groups to protect their values within a democratic society. Which specific perceptions generate such a triggering event, which value-protective responses does it trigger, and do such responses escalate intergroup conflict? We offer the intergroup value protection model to analyze the moral and group psychology of intergroup conflict escalation in democratic societies. It predicts that when group members cognitively interpret another group's actions as violating ingroup or shared values, this triggers the intergroup value protection process (e.g., increased ingroup identification, outrage, moralization, social protest). When such value-protective responses are visible to the outgroup, this can in turn constitute a trigger event for them to protect their values, thus increasing chances of intergroup conflict escalation. We discuss scientific implications and practical challenges for managing intergroup value conflict in democratic societies, including fears of societal breakdown and scope for social change.

Intergroup conflict as contest and disease.

Intergroup conflict has been conceptualized as a strategic interaction (conflict-as-contest) and separately as a pathological condition (conflict-as-disease). We highlight how insights and tools from the former perspective can potentially inform the latter. Harnessing the science of strategic decision-making can facilitate the development of novel approaches for mitigating intergroup conflict.

Can Peripheral Group Members Not Represent the In-Group? The Effect of Member Prototypicality on Intergroup Conflict.

Group member prototypicality is a factor in intergroup conflict-not all group members fight for group interests. This study focuses on the role of peripheral group members and the factors that influence their participation. We conducted two studies to examine the effects of group acceptance and self-uncertainty on the relationship between prototypicality and intergroup conflict. Results indicate that group acceptance moderates the relationship between prototypicality and intergroup conflict. Self-uncertainty moderates the effect of the interaction between prototypicality and group acceptance on intergroup conflict. Our findings have theoretical and practical implications for intergroup conflict resolution.

Timing is everything: Developmental changes in the associations between intergroup contact and bias.

Identifying developmental patterns in intergroup contact and its relation with bias is crucial for improving prevention strategies around intergroup relations. This study applied time-varying effects modeling (TVEM) to examine age-based changes in relations between contact and bias in a divided community that included 667 youth (M age = 15.74, SD = 1.97) from Belfast, Northern Ireland, a conflict-affected setting. The results suggest no change in the relation between contact frequency and bias; however, the relation between contact quality and bias increases from ages 10-14 and then levels off. Differences between Catholics, the historic minority group, and Protestants, the historic majority group, also emerged. The article concludes with implications for future research and interventions for youth growing up amid conflict.

A collective neuroscience lens on intergroup conflict.

How do team leaders and followers synchronize their behaviors and brains to effectively manage intergroup conflicts? Zhang and colleagues offered a collective neurobehavioral narrative that delves into the intricacies of intergroup conflict. Their results underscore the importance of leaders' group-oriented actions, along with leader-follower synchronization, in intergroup conflict resolution.

Exploring the Influence of Perceived Ingroup and Outgroup Threat on Quality of Life in a Region Impacted by Protracted Conflict.

While the detrimental effects of protracted political conflict on the wellbeing of Palestinians living in the occupied Palestinian territory (oPt) are generally recognized, the impact of perceived threat on quality of life (QoL) faced from within their community (ingroup; Palestinians) and from the outgroup (Israelis) is unexplored. This cross-sectional study examined the following: (1) The status of perceptions of QoL on four domains measured by the World Health Organization Quality of Life (WHOQoL-Bref) instrument, physical health, psychological health, social relationships, and environment, among Palestinian adults (n = 709) living in the Gaza Strip; (2) The associations between perceived ingroup threat (PIT) and QoL on the four domains; (3) The associations between perceived outgroup threat (POT) and QoL on the four domains. Multivariable linear regression models revealed PIT was negatively associated with QoL in each of the four domains (p < 0.001). POT was positively associated with QoL in three of the four domains: physical health (p < 0.001), psychological health (p < 0.001), and social relationships (p < 0.001). This study contributes valuable insights into how QoL is viewed by a group experiencing collective existential threat. The findings expand the limited recognition of the reciprocal roles of perceived threat from the ingroup and outgroup on the QoL of vulnerable populations.

Double trouble: How sectarian and national narcissism relate differently to collective violence beliefs in Lebanon.

Collective narcissism is a belief in ingroup greatness which is contingent on external validation. A lack of research on collective narcissism amongst non-Western contexts and minority groups remains a challenge for the field. However, here we test two types of collective narcissism (sectarian and national) as differential predictors of two dimensions of collective violence beliefs (against outgroup members and leaders) in a large, diverse, community sample from Lebanon (N = 778). We found that sectarian narcissism (narcissism related to smaller political and religious ingroup identity) predicted support for collective violence against members of different sects, while national narcissism predicted opposition to such collective violence. Neither form of collective narcissism had any significant relationship with collective violence against outgroup leaders. We controlled for both sectarian and national identification and found no significant effects in predicting either one of the two dimensions of collective violence beliefs. In this non-Western context, in which a coherent national identity is undermined by sectarianism, national narcissism seems to be a progressive motivator for unity and social change, while sectarian narcissism is rather associated with extreme attitudes, such as support for collective violence.

The process of becoming 'we' in an intergroup conflict context: How enhancing intergroup moral similarities leads to common-ingroup identity.

Research on common-ingroup identity has mainly focused on consequences and potential benefits of inclusive social categorizations. However, very little is yet known about processes and conditions that could facilitate such inclusive social categorizations. In this paper, with four studies (N = 582) set in a post-conflict context of Bosnia and Herzegovina and with members of two ethnic groups (Bosniaks and Serbs), we have demonstrated how perceptions of intergroup moral similarity can act as an important precursor of common-ingroup identity at the national level. We report both cross-sectional as well as experimental evidence demonstrating how perceptions of intergroup moral similarity boost common-ingroup identifications in socially relevant context using members of real adversary social groups. Moreover, we show that learning about outgroups' morally admirable behaviours can facilitate inclusive social categorizations.

The evolution of intergroup cooperation.

Sociality is widespread among animals, and involves complex relationships within and between social groups. While intragroup interactions are often cooperative, intergroup interactions typically involve conflict, or at best tolerance. Active cooperation between members of distinct, separate groups occurs very rarely, predominantly in some primate and ant species. Here, we ask why intergroup cooperation is so rare, and what conditions favour its evolution. We present a model incorporating intra- and intergroup relationships and local and long-distance dispersal. We show that dispersal modes play a pivotal role in the evolution of intergroup interactions. Both long-distance and local dispersal processes drive population social structure, and the costs and benefits of intergroup conflict, tolerance and cooperation. Overall, the evolution of multi-group interaction patterns, including both intergroup aggression and intergroup tolerance, or even altruism, is more likely with mostly localized dispersal. However, the evolution of these intergroup relationships may have significant ecological impacts, and this feedback may alter the ecological conditions that favour its own evolution. These results show that the evolution of intergroup cooperation is favoured by a specific set of conditions, and may not be evolutionarily stable. We discuss how our results relate to empirical evidence of intergroup cooperation in ants and primates. This article is part of a discussion meeting issue 'Collective behaviour through time'.

From Threat to Challenge: Understanding the Impact of Historical Collective Trauma on Contemporary Intergroup Conflict.

Collective memories of trauma can have profound impact on the affected individuals and communities. In the context of intergroup conflict, in the present article, we propose a novel theoretical framework to understand the long-term impact of historical trauma on contemporary intergroup relations from both victim and perpetrator perspectives. Integrating past research on intergroup conflict and the biopsychosocial model of threat and challenge, we argue that people appraise their group's past victimization and perpetration differently, either as a threat or as a challenge. Shaped by contextual factors and individual differences, these differential appraisals will subsequently influence how group members respond to contemporary intergroup conflict, with both adaptive and maladaptive consequences. This model contributes to unifying the previous research that has shown diverse effects of historical trauma on present-day intergroup dynamics. We present preliminary empirical evidence in support of the framework and discuss its theoretical and practical implications.

Protected by the Emotions of the Group: Perceived Emotional Fit and Disadvantaged Group Members' Activist Burnout.

Psychological processes that hamper activism, such as activist burnout, threaten social change. We suggest that perceived emotional fit (i.e., perceiving to experience similar emotions as other disadvantaged group members) may buffer activist burnout by mitigating the deleterious effects of stressors that are associated with partaking in collective action. We investigated the relation between perceived emotional fit and activist burnout using three-wave longitudinal survey data of Palestinians in the context of the Palestinian-Israeli conflict. We hypothesized that both higher general tendencies to fit emotionally with the ingroup (general perceived emotional fit) and increases over time in perceived emotional fit (change perceived emotional fit) would relate negatively to activist burnout. Supporting our hypotheses, both aspects of emotional fit were associated with lower activist burnout, even when controlling for classical predictors of collective action. This research highlights perceived emotional fit as an additional dimension to the role of emotions for sustainable collective action.

Individuals prefer to harm their own group rather than help an opposing group.

Group-based conflict enacts a severe toll on society, yet the psychological factors governing behavior in group conflicts remain unclear. Past work finds that group members seek to maximize relative differences between their in-group and out-group ("in-group favoritism") and are driven by a desire to benefit in-groups rather than harm out-groups (the "in-group love" hypothesis). This prior research studies how decision-makers approach trade-offs between two net-positive outcomes for their in-group. However, in the real world, group members often face trade-offs between net-negative options, entailing either losses to their group or gains for the opposition. Anecdotally, under such conditions, individuals may avoid supporting their opponents even if this harms their own group, seemingly inconsistent with "in-group love" or a harm minimizing strategy. Yet, to the best of our knowledge, these circumstances have not been investigated. In six pre-registered studies, we find consistent evidence that individuals prefer to harm their own group rather than provide even minimal support to an opposing group across polarized issues (abortion access, political party, gun rights). Strikingly, in an incentive-compatible experiment, individuals preferred to subtract more than three times as much from their own group rather than support an opposing group, despite believing that their in-group is more effective with funds. We find that identity concerns drive preferences in group decision-making, and individuals believe that supporting an opposing group is less value-compatible than harming their own group. Our results hold valuable insights for the psychology of decision-making in intergroup conflict as well as potential interventions for conflict resolution.

Distinguishing Intergroup and Long-Distance Relationships.

Intergroup and long-distance relationships are both central features of human social life, but because intergroup relationships are emphasized in the literature, long-distance relationships are often overlooked. Here, we make the case that intergroup and long-distance relationships should be studied as distinct, albeit related, features of human sociality. First, we review the functions of both kinds of relationship: while both can be conduits for difficult-to-access resources, intergroup relationships can reduce intergroup conflict whereas long-distance relationships are especially effective at buffering widespread resource shortfalls. Second, to illustrate the importance of distinguishing the two relationship types, we present a case study from rural Bolivia. Combining ethnography and two different experimental techniques, we find that the importance of intergroup relationships-and the salience of group membership itself-varies across populations and across methods. Although ethnography revealed that participants often rely on long-distance relationships for resource access, we were unable to capture participant preferences for these relationships with a forced-choice technique. Taken together, our review and empirical data highlight that (1) intergroup and long-distance relationships can have different functions and can be more or less important in different contexts and (2) validating experimental field data with ethnography is crucial for work on human sociality. We close by outlining future directions for research on long-distance relationships in humans.