The Fusion-Secure Base Hypothesis

The Conditional Violence of Identity Fusion

Fusion’s most salient feature is arguably its tendency to predict violence toward out-groups, particularly via self-sacrificial attacks (Whitehouse, 2018a). An increased willingness among fused actors to fight and die for the group has been demonstrated multiple times, correlationally (Buhrmester et al., 2015; Gomez, Brooks, et al., 2011), experimentally (Swann, Gomez, Dovidio, et al., 2010; Swann et al., 2009; Swann, Gomez, Huici, et al., 2010), and across a range of contexts. Fusion has been implicated in intertribal violence in Cameroon (Buhrmester et al., 2022), retaliation against the 2015 Palestinian Stabbing intifada (Fredman et al., 2017), the formation of violent Viking war bands (Raffield et al., 2015), and suicide bombings (Whitehouse, 2018a). Although some have alleged fusion is conceptualized as being synonymous with violence (Kiper & Sosis, 2018; Xygalatas, 2018), most research suggests that fusion only predicts out-group hostility in the context of threat.

The moderating role of threat underlies a prominent evolutionary account of fusion as psychological machinery that allowed highly cohesive bands of individuals to form in humanity’s Paleolithic past and collectively ward off threats (Whitehouse, 2018a), and has been demonstrated multiple times empirically. For instance, devoted actors—individuals fused to a group with embedded sacred (i.e., nonnegotiable) values (see Atran, 2016)—are more willing to engage in costly sacrifices than nondevoted actors, but only when threatened (Sheikh et al., 2016). Specifically, Sheikh et al. (2016) found that Spaniards were most willing to endorse violent pro-group actions if they were fused with their friends, considered democracy to be a sacred value, and had been reminded of the 2004 terrorist train bombings in Madrid. Devoted actors were also more inclined to behave aggressively toward representations of an out-group in a video game, but only when the out-group was primed as threatening (Vazquez et al., 2020). Similarly, a longitudinal study during a stabbing intifada in Israel found that fusion to Judaism became a stronger predictor of hostility toward Palestinians as violence increased (Fredman et al., 2017), while fused football hooligans were more likely than fused mainstream fans to have engaged in violence against rival football fans, possibly explained by the fact that football hooligans are exposed to more frequent and intense threats than mainstream fans (Newson et al., 2018). Even the commonly used willingness to fight and die for the group scale asks the respondent to endorse violent actions in the context of an explicit threat to the group in most items (e.g., “I would physically fight someone threatening another group member”; Swann et al., 2009). Fusion’s relationship with violence is clearly dependent upon the perception of threats to the group.

Moreover, these violent actions tend to be directed at the source of the threat (i.e., not indiscriminate) and influenced by group norms. For instance, fusion among football hooligans was a significant predictor of violence against rival fans, but not other targets (e.g., police, family members), suggesting that the retaliatory behaviors of fused hooligans were aimed at the source of threat (Newson et al., 2018). Even in the case of threatened fused actors, violent actions are not inevitable. Chinchilla et al. (2021) found that the positive relationship between fusion and violent—but not nonviolent—pro-group behavior was moderated by moral beliefs, such that fusion only predicted willingness to engage in violence among those with a belief in the justifiability of violence. This reflects research on Lebanese Sunni, Shia, and Christian Maronites that found that the relationship between fusion to religion and a willingness to engage in parochial pro-group sacrifices (e.g., risking the safety of their family to fight for the group) was moderated by moral concerns; fused actors who valued parochial attitudes (e.g., respect for authority) over universal values (e.g., concern for others) were more inclined to make parochial sacrifices (Sheikh et al., 2014). Of course, the fused group’s own norms and ideology also matter in determining the likelihood of violent retribution. For instance, the religion of Jainism is marked by its extreme promotion of nonviolence to the detriment of the self (e.g., some Jains are unwilling to engage in agriculture due to a fear of killing small insects; Sen, 2014). Fusion to a Jainist sect would likely be a strong negative predictor of willingness to commit violence in most circumstances, suggesting that fusion is not inevitably linked to aggression. Fused actors are hence not necessarily more violent than their nonfused counterparts, with personal values and group norms dictating the type of retribution administered to threatening out-groups.

To date, almost all research on fusion and intergroup relations has been conducted in the context of a threatening out-group, either nonspecified (e.g., research that uses the willingness to fight and die for the group scale) or specified (e.g., Newson et al., 2018; Vazquez et al., 2020). However, there is little research on how fused actors respond to an out-group that is not viewed as threatening or in an antagonistic relationship with the in-group. While the idea that identity fusion—a construct originally devised to explain suicidal terrorist attacks—may have positive implications for intergroup relations might seem far-fetched, attachment theory sheds light on a potential mechanism through which this could occur. At its core, identity fusion is an extreme form of group alignment marked by a deep sense of connection to a group and its members (Swann & Buhrmester, 2015), enabling a reliable and extraordinary source of collective security in which each member is valued as a unique individual. This combination provides the fused actor with a secure base, which has been demonstrated to have positive implications for intergroup relationships (Tropp, 2021). Relatedly, high levels of in-group trust, such as that between fused group members, can be projected outward through an increased trust of out-group members (Delhey & Welzel, 2012), while self-affirmation experiences, in which the worth of the self is made salient, have been linked to a willingness to engage with out-group members (Badea & Sherman, 2018). Contextualizing identity fusion within attachment theory provides a range of novel predictions, including the suggestion that fusion might improve intergroup trust and cooperation.

A Secure Base Increases Exploration, Trust, and Cooperation

The idea of a secure base has its origins in Bowlby’s attachment theory, which emphasizes the importance of closeness in caregiver–child relationships (Waters et al., 2002). Children build mental models of the self and others from experiences with their caregiver; if the needs of the child are met, then the caregiver is recognized as a secure base and empowers feelings of competency and a willingness to explore away from the attachment figure (Waters et al., 2002). Continual positive interactions with a secure base contribute to the development of a secure base schema—a set of positive expectations about the availability and responsiveness of an attachment figure (Mikulincer, Hirschberger, et al., 2001)—that allow a child to more confidently interact with their environment. Correspondingly, the absence of a secure base can engender an insecure attachment style, namely, attachment-anxiety (i.e., anxious, uncertain, and clingy) or avoidance (i.e., emotionally distant, averse to affection), which may limit feelings of security and willingness to explore (Green & Campbell, 2000). The positive effects of a secure base are manifested in two distinct ways: the safe-haven and secure-base functions. The safe-haven function refers to the tendency of a secure base to instill felt security through protecting the attached person from potential threats and responding to signals of distress (Collins & Ford, 2010). By contrast, the secure-base function refers to the support, encouragement, and recognition given to the attached person by an available and dependable attachment figure, augmenting their sense of autonomy and capacity to confidently explore their environment (Collins & Ford, 2010). Both functions collectively consolidate the attached person’s sense of security, emboldening them to face novel challenges and social environments; the presence of an attentive attachment figure has been demonstrated to reduce fear of strangers in infants (Sorce & Emde, 1981), while securely attached children engage in more positive interactions with strangers (Moss et al., 1997).

Attachment figures are similarly relied upon for comfort and stress reduction among securely attached adults (Collins & Feeney, 2000). Adult attachment figures are most commonly conceptualized as romantic partners (Feeney, 2004; Feeney & Thrush, 2010), but military leaders (Davidovitz et al., 2007), social institutions (Mayseless & Popper, 2007), God (Kirkpatrick, 2005), therapists (Shaver & Mikulincer, 2008), and, most importantly, groups (Rom & Mikulincer, 2003; Smith et al., 1999) can all operate as secure bases. A secure base schema expands an individual’s ability to positively engage with strange, ambiguous, or distressing stimuli and has been found to predict more optimistic threat appraisals and better stress-coping (Mikulincer & Florian, 1998) and a tendency to interpret a romantic partner’s behavior more positively (Collins, 1996; Collins & Feeney, 2004). Interestingly, a secure base schema can be contextually activated (e.g., Baldwin, 1994) even in those who ordinarily have an insecure attachment style (Baldwin et al., 1996). For example, priming a secure base schema has been shown to increase cognitive openness to new information (Mikulincer & Arad, 1999) and empathy and reduce distress (Mikulincer, Gillath, et al., 2001). A secure base hence acts as a reservoir of support and encouragement, emboldening others to freely interact with the outside world.

A secure base schema also allows people to better manage their interactions and relationships with others. Securely attached persons have reported a generally more pro-social orientation (Feeney & Collins, 2001) and demonstrated increased compassion (Florian et al., 2000) and responsiveness to others’ suffering (Westmaas & Silver, 2001). Adolescents with a secure peer friendship group have been found to report engaging in more pro-social behavior (e.g., a tendency to be kind to others) and fewer emotional difficulties and conduct problems (e.g., anger proneness), with these relationships largely mediated by dispositional empathy, further suggesting that a secure base can promote positive interpersonal relations (Schoeps et al., 2020). In interpersonal disputes, securely attached individuals have been found to be more integrative and compromising (Corcoran & Mallinckrodt, 2000; Shi, 2003), use more supportive and validating behavior (Creasey, 2002; Kobak & Hazan, 1991; Simpson et al., 1996), express more respect and positive affect (Wampler et al., 2003), discuss a problem until it is solved (Corcoran & Mallinckrodt, 2000), respond more adaptively to anger episodes and be less prone to anger (Mikulincer, 1998a), be less willing to use coercion (Creasey, 2002), and demonstrate more skillful problem-solving (Mikulincer & Sheffi, 2000) and conflict resolution (Creasey et al., 1999). These superior conflict management skills are largely driven by a belief that others are kind and well intentioned (Hazan & Shaver, 1987), and their own sense of self-efficacy (Corcoran & Mallinckrodt, 2000), both stemming from a strong secure base schema.

A related body of research suggests that belonging to a secure base increases the trust of others, including strangers. A secure base schema has been associated with an increased willingness to trust actual and hypothetical romantic partners (e.g., Brennan & Shaver, 1995; Hazan & Shaver, 1987), the expectation that trust will result in positive outcomes (Baldwin et al., 1993, 1996), greater accessibility of positive trust-related memories, and more constructive ways of coping with trust violations (Mikulincer, 1998b). Securely attached people have also reported more trust in their work supervisor, which in turn had a positive effect on work performance, suggesting that a secure base allows people to focus on the task at hand without having to worry about “watching their back” (Simmons et al., 2009). Collins and Read (1990) found that securely attached adults had a stronger belief in: the integrity of social role agents (e.g., the judiciary), the trustworthiness of human motives, the dependability of others, and trustworthiness as a part of human nature. Relatedly, the warmth of their relationship with their mother or father positively predicted their belief in the dependability of people (Collins & Read, 1990). This research collectively suggests that positive experiences with a secure base “spill-over” onto others, causing securely attached persons to trust strangers more willingly.

This, in turn, manifests itself in an increased tendency to explore new social opportunities. Building on work that demonstrated a secure attachment style predicted increased exploratory behavior in children (e.g., Ainsworth & Bell, 1970) and that secure attachment in adults was associated with increased curiosity and openness to accepting and integrating new information (Mikulincer, 1997), Green and Campbell (2000) examined whether a secure base could increase exploratory behaviors in adults. They found that adults with greater chronic attachment anxiety or avoidance expressed less interest in exploratory activities (e.g., “I would like the chance to meet strangers,” “I would like to explore the ideas of foreign cultures”) and that priming a secure base schema similarly increased interest in exploratory behaviors. This relationship appears to be mediated by perceptions of social support, such that attachment avoidance negatively predicted social and intellectual exploration via perceived support from the participant’s mother or best friend (Wu & Yang, 2012), further indicating that a secure base promotes exploration. Observational research has similarly found that the endorsement of exploratory behaviors (e.g., “I am usually willing to accept challenges and try new things”) was positively predicted by the degree to which a present romantic partner was perceived to be a secure base (Feeney, 2004) and that participant self-reported and observed responsiveness and sensitivity to distress cues predicted their romantic partner’s engagement in a novel exploration activity and success at exploring a personal goal 6 months later (Feeney, 2007). A further observational study on romantic couples found that three theorized components of a secure base—availability, noninterference, and encouragement/acceptance of exploration—each strongly predicted increased exploration of a novel task (Feeney & Thrush, 2010), suggesting that a secure base encourages constructive behavior in unfamiliar contexts. In sum, a secure base enables people to manage relationships, trust others, and explore new environments and social opportunities, suggesting that a secure base schema may also compel people to explore relationships with out-group members.

A Secure Base Improves Intergroup Relations

It is worth considering intergroup relationships separately from interpersonal relationships, as the former are particularly likely to be marked by anxiety and distrust. A general reluctance to interact with out-group members has been demonstrated in multiple studies: Ethnic majority members preferred neighborhoods with fewer ethnic minority members, even controlling for crime rate and housing quality (Schlueter et al., 2018), school students segregated along ethnic lines in the school cafeteria (Ramiah et al., 2015), and Protestant and Catholic residents of Belfast, despite often living in close proximity, rarely visited out-group areas and preferred the streets and facilities of their in-group’s residential areas (Dixon et al., 2020). Contact avoidance often implies the presence of intergroup anxiety, defined as a visceral fear of out-group contact (Stephan, 2014). Intergroup anxiety typically stems from a perceived realistic or symbolic out-group threat (Stephan, 2014), with fear responses to out-group members more readily learned and resistant to extinction (O’Donnell et al., 2019). This has been shown to have a deleterious effect on intergroup relations. For example, students with higher levels of intergroup anxiety toward other ethnicities at the end of the first year of college had fewer ethnic out-group friends during their second and third years of college (Levin et al., 2003), while Black South African high school students that reported high intergroup anxiety toward White South Africans had fewer cross-group friendships 6 months later, which in turn led to more intergroup anxiety a further 6 months later (Swart et al., 2011). In short, people tend to prefer interacting with members of their in-group, and intergroup anxiety acts as a major barrier to intergroup relations.

There is, however, evidence to suggest that a supportive and protective in-group can act as a secure a base (Mikulincer & Shaver, 2017; Smith et al., 1999) and assist its members in overcoming intergroup anxiety (Kauff et al., 2020), thereby facilitating the development of cooperative intergroup relationships. Belonging to a group is a fundamental human need, with attachment systems likely having evolved to regulate group relationships (Baumeister & Leary, 1995). Smith et al. (1999) found that people’s experiences with groups give rise to mental models of group memberships, which in turn guide perceptions of, and interactions with, other groups. This perspective suggests that a caring and a supportive group can act as a secure base (Smith et al., 1999), thereby imprinting a secure base schema onto even the insecurely attached (Mikulincer & Shaver, 2017). For example, group cohesiveness among soldiers has been found to improve the socioemotional (i.e., behaviors that contributed to a positive group environment and social relations) and instrumental (i.e., behaviors that contributed to a successful completion of the mission) functioning during a mission and acted as a psychological buffer against the detrimental effects of global attachment anxiety on instrumental functioning and group attachment (Rom & Mikulincer, 2003). Similarly, anxiously attached first-year university students who participated in a transition facilitation group reported better academic and emotional outcomes 6 months later than students in a control condition (Ames et al., 2011), while the cohesiveness of a psychotherapy group predicted reduced eating disorder symptomology among anxiously attached participants (Gallagher et al., 2014). These results suggest that belonging to a supportive and cohesive group can override dispositional attachment styles, particularly among the anxiously attached, and instill participants with a secure base schema (Mikulincer & Shaver, 2017).

Moreover, evidence from the social identity theory literature suggests that a strong group identity can improve relationships with out-groups. For example, a series of studies on residential mixing in Northern Ireland and England found that a supportive group can help individuals overcome intergroup anxiety. Stevenson et al. (2019) found in a Northern Irish sample that a strong sense of community with the local neighborhood predicted lower negative out-group attitudes via a reduction in intergroup anxiety. These results were then replicated in a specific East Belfast neighborhood in which neighborhood identity, directly and indirectly, predicted better intergroup attitudes; interestingly, mixing with the out-group by itself was not associated with reduced intergroup anxiety. Stevenson et al. (2020) demonstrated that the effect of neighborhood identification on reduced intergroup anxiety is mediated by perceptions of community support, which a subsequent study found increased feelings of collective confidence and out-group contact (Stevenson et al., 2021). Similar studies have also found that strong in-group identification can improve out-group relations: A more secure and mature ethnic identity was associated with significantly more open and positive attitudes toward other ethnic groups (Phinney et al., 2016), adolescents who were more identified with an in-group made more positive evaluations about the preferences of an out-group, but only in a context that was not threatening to their social identity (Tarrant et al., 2004), and secure in-group identification with Poland predicted positive attitudes toward Ukrainians, especially when controlling for collective narcissism (Marchlewska et al., 2020). These studies suggest that belonging to a supportive group reduces intergroup anxiety via perceptions of a secure base which in turn can increase confidence in out-group interactions, thereby improving intergroup relations.

There is also evidence that high levels of in-group trust can be projected outward, resulting in greater out-group trust. Data from the fifth round of the World Values Survey indicated that in-group trust (e.g., trust of your family and neighborhood) was positively associated with out-group trust (e.g., people of another religion and nationality; Welzel, 2010) and that both are distinct dimensions of trust (i.e., not merely a part of the same trust continuum; Delhey et al., 2011). Building on these results, Delhey and Welzel (2012) used the survey to compare the strength of out-group trust borne out of in-group trust (the projection route) versus out-group trust created independent of out-group trust (the creation route) by entering potential predictors of out-group trust (e.g., gross domestic product [GDP], emancipative values) into 18 regressions controlling for in-group trust or vice versa (Delhey & Welzel, 2012). The projection route contributed more to the generation of out-group trust than the creation route in almost every regression, strongly implying that in-group trust has a large, positive influence on out-group trust and that high levels of in-group trust—as is present in a highly cohesive group—could increase the trust of out-group members.

Relatedly, self-affirmation theory suggests that alignment with a supportive secure base, particularly one that fosters its member’s self-integrity, could reduce out-group prejudice. People are motivated to maintain self-integrity (i.e., to see oneself as good or virtuous), particularly in the face of threats to the personal or social self (e.g., negative feedback on an exam, evidence of the in-group’s moral wrongdoings), and that denigrating an out-group can help restore it (Badea & Sherman, 2018). However, if self-integrity is restored via self-affirmation—an act that demonstrates personal adequacy (e.g., being cared for by friends or family, a personal achievement, recognizing one’s values)—then there is a reduced need to restore it via prejudice (Cohen & Sherman, 2014). Self-affirmation interventions have repeatedly been shown to reduce defensiveness (Cehajic-Clancy et al., 2011; Gunn & Wilson, 2011) and prejudice (Badea et al., 2018) and promote positive and constructive engagement with out-group members (Badea et al., 2017; Stone et al., 2011), particularly among those with a salient collective identity (Cohen et al., 2007). A strong and supportive social network (i.e., a secure base) could be expected to provide frequent opportunities for self-affirmation, such as through positive feedback and rewards (Cohen & Sherman, 2014), thereby buffering against the threat, limiting defensiveness, and ultimately reducing negative attitudes toward out-groups.

While the studies mentioned so far have primarily focused on groups that are assumed to act as a secure base, the positive effects of a secure base on intergroup relations have also been demonstrated via a priming paradigm. Mikulincer and Shaver (2001) primed a secure base schema in Israeli participants across five studies through exposure to subliminal words related to security (e.g., love, support) and guided imagination tasks (e.g., imagine that you are surrounded by people who are sensitive and responsive to your distress, want to help you only because they love you, and set aside other activities to assist you). Participants were then asked to evaluate an out-group member (e.g., an Arab student, a homosexual, an Orthodox Jew). Secure base priming attenuated negative evaluations of out-group members such that participants in the secure base conditions reliably felt almost equally positive about in-group and out-group participants, while participants in the neutral-control conditions (e.g., exposed to words unrelated to attachment such as table, primed to visualize a person in the neighborhood they don’t know well) or positive-affect condition (e.g., exposed to words with a positive affective connotation such as success, visualized a person who is always happy and loves fun and jokes) were significantly warmer only toward in-group members. This effect was maintained even controlling for dispositional attachment style and mood and was mediated by a reduced threat appraisal of out-group members.

The authors replicated these effects across several follow-up studies. Mikulincer et al. (2005) found that priming a secure base schema in Israelis and Americans led to greater compassion and inclination to help a woman in distress, even when there was no egoistic reason (e.g., mood relief) to help. Although securely primed participants were most willing to help the woman if she was a family member, they were still more helpful than control participants even if the woman was someone they did not know well. The research described in Mikulincer and Shaver (2007) found that Israeli Jews who were subliminally primed with a named attachment figure (e.g., best friends) allocated a similarly low amount of painful hot sauce to Israeli Jews (i.e., in-group) and Arabs (i.e., out-group) members, whereas those not primed with an attachment figure allocated significantly more hot sauce to out-group members. Saleem (2011) similarly found that participants primed with a secure base schema had a lower implicit bias against Arabs (i.e., out-group), versus insecurely primed or neutral-primed participants. Moreover, the effect of priming on prejudice was moderated by identification with the United States (i.e., in-group), with the secure prime only reducing out-group prejudice among highly identified Americans. This suggests that perceptions of a secure base can resolve tensions even when an antagonistic intergroup relationship exists and may work best on those who are most strongly aligned to the group. Together, these results indicate that a secure base, in which one feels loved and supported, lends itself to reduced negative (e.g., Saleem, 2011) and increased positive (e.g., Mikulincer & Shaver, 2001) attitudes toward the out-group.

Most crucially, however, a secure base also directs increased exploratory behavior. Boccato et al. (2015) found that a secure attachment style in Italian natives negatively predicted implicit prejudice against immigrants (i.e., out-group) but also positively predicted the quality and quantity of out-group contact via a greater openness to social exploration (e.g., a willingness to meet new people). The quality of out-group interactions in turn positively mediated the relationship between secure attachment and out-group evaluations, suggesting that, while a secure base allows for intergroup interaction opportunities, it is the quality of these interactions that ultimately determine intergroup relations. Mikulincer and Shaver (2001) similarly found that priming a secure base in secular Jews led to an increased willingness to interact with (e.g., invite them to your home, have them accompany you and your friends) an ultraorthodox Jew (i.e., out-group member) versus a positive or neutral prime. These results, along with similar findings in an interpersonal context (e.g., Feeney, 2004; Feeney & Thrush, 2010; Green & Campbell, 2000; Wu & Yang, 2012), strongly suggest that a secure base opens people to new social opportunities they are emboldened to act upon.

The work outlined thus far strongly suggests that alignment to a group—particularly one that is benevolent and kind to its members—should engender a secure base schema in which one feels supported and encouraged to explore and interact with out-groups. Much of this evidence has drawn upon social identity theory (see Tajfel & Turner, 2004), suggesting that strong identification with an in-group could increase the likelihood of intergroup cooperation. Although any type of group alignment could theoretically lead to a secure base schema, there are reasons to believe that identity fusion is a particularly potent candidate. The attachment literature suggests that an effective secure base reliably offers protection, comfort, and relief from distress while also providing a supportive and encouraging environment that drives exploration and goal achievement (Bowlby, 1982). Identity fusion certainly fits this definition; fusion’s evolutionary origin centers around collective security, while each of fusion’s four key principles (i.e., the relational ties principle, irrevocability principle, agentic-personal-self principle, and identity synergy principle) feed into perceptions of protection, comfort, and support. The following section makes the theoretical case that a fused group acts as a particularly secure base, and that fusion is more likely to engender a secure base schema than other forms of group alignment.

The Fusion-Secure Base Hypothesis

Drawing on the link between a secure base schema and positive intergroup interactions observed in the attachment literature (e.g., Tropp, 2021), the fusion-secure base hypothesis (see Figure 1) argues that fused actors should be more willing to approach, trust, and cooperate with unknown or benign out-group members. This is the result of dual safe-haven and secure-base functions which promote a sense of safety and support respectively, thereby empowering fused actors to explore intergroup relationships and engage in cooperation with out-groups. In line with other theorists who highlight the inherent psychological costs associated with fusion that prohibit fusion with multiple groups (e.g., Swann et al., 2012), we do not argue that fusion with one group predicts fusion with other, unnested groups. Rather, we suggest that—all else being equal—a fused actor is more likely to trust and cooperate with an out-group member than an unfused person, emboldened by their secure base. This extends Brewer’s (1999) contention that in-group love is independent of out-group hate (originally applied to group identification) to the fusion literature; in this context, in-group love is conceptualized as a predictor of out-group trust and cooperation.

OPEN IN VIEWER

Figure 1.

Model diagram of the fusion-secure base hypothesis.

The fusion-secure base hypothesis ultimately argues that fusion has a strong influence on intergroup dynamics, predicting both intergroup cooperation (via a secure base schema) and conflict (in the context of threat). In fact, many of the same fusion qualities that promote aggression toward out-groups in hostile contexts likely also increase intergroup cooperation in more benign settings. For example, fusion has been found to increase agency, which in turn predicted a willingness to fight and die for the group among fused actors (Swann, Gomez, Huici, et al., 2010). However, increased agency is also associated with a secure-base schema (Dilmac et al., 2009; Hashworth et al., 2021; Hexel, 2003; Mickelson et al., 1997; West & George, 2002) and has been found to strongly predict cooperation (Boone et al., 1999, 2002; Boone & De Brabander, 1999), suggesting that a fusion outcome traditionally associated with out-group violence (i.e., agency) could be redirected to promote out-group cooperation. Feelings of personal agency and recognition of goal achievement by the group are also likely to represent instances of self-affirmation (Cohen & Sherman, 2014), thereby further reducing defensiveness and hostility toward out-groups. The relationship between fusion and out-group violence has similarly been mediated by invulnerability (Gomez, Brooks, et al., 2011), mirroring attachment research which has linked a secure-base schema to: a propensity to cope with adversity (Caputo et al., 2020), reduced fear of strangers (Sorce & Emde, 1981), optimistic threat and death appraisals (Mikulincer & Florian, 1998, 2000), and perceptions of symbolic immortality (Florian & Mikulincer, 1998). In the same way that a sense of invulnerability spurs a fused actor to fearlessly fight threatening out-groups, the attachment literature suggests that it could reduce intergroup anxiety and facilitate interactions with out-groups. Finally, the immense trust between group members inherent in the familial bonds that have mediated fusion’s link to violent progroup behaviors (Swann, Buhrmester, et al., 2014) could “spill over” onto out-group members (e.g., Delhey & Welzel, 2012), thereby increasing a fused actor’s level of general trust (i.e., a person’s propensity to trust others across situations; Van Lange, 2015) and trust of out-group members. Feeling trusted and cared for by close others may similarly affirm the self (Cohen & Sherman, 2014), also promoting positive intergroup relationships. Hence, the very same dynamics that drive fusion’s violent qualities may, in the absence of an out-group threat, be redirected toward intergroup trust and cooperation.

The idea that fusion can increase the likelihood of both violence and cooperation reflects a key principle of the fusion-secure base hypothesis; specifically, that fusion is not a predictor of prosociality per se, but rather predicts a willingness to engage with out-groups in whatever way most benefits the self and the in-group. This is in line with empirical evidence showing that fused actors consider their interactions with out-groups primarily in terms of benefits to the in-group. For example, fused actors have been found to endorse harming out-groups, but only in a context in which this maximized the in-group’s chances of winning a hypothetical competition (Buhrmester, Newson, et al., 2018). Moreover, if the heightened personal agency of fused actors does promote intergroup cooperation, research indicates that this should only occur in situations where intergroup cooperation is a better strategy than conflict (Boone et al., 1999), reflecting the increased capacity of agentic people to learn from their environment (Boone et al., 2002). This suggests that the types of intergroup relationships fusion can engender are likely based on equality matching (i.e., one-for-one reciprocation) or market pricing (i.e., interactions based on a rate or ratio) principles (Fiske, 2004), which describe mutually beneficial interactions rather than indiscriminate out-group prosociality. Fusion could also conceivably predict an intergroup relationship based on authority ranking (i.e., ordered differences between groups), focused on extracting maximum benefit from an out-group (Fiske, 2004), although this would likely depend on the out-group being weaker than the in-group and the culture of the in-group endorsing oppressive behaviors, such as slavery or extortion. However, while there are undeniably many examples of powerful groups subjugating vulnerable out-groups throughout history, the attachment literature consistently emphasizes the cooperative advantages of a secure base in intergroup contexts (e.g., Tropp, 2021) and so we similarly highlight intergroup cooperation in the fusion-secure base hypothesis.

There are several theoretical clarifications regarding the model that are worth discussing upfront, such as whether fusion with the in-group should predict cooperation with any out-group. Although the model should apply to any conceivable out-group member (e.g., a stranger and foreigner), fused actors may have a particularly strong rationale to cooperate when the in-group and out-group are at equivalent levels of abstraction (e.g., two communities and two nations). This is because “equivalent” groups are more likely to face similar problems and have similar goals, which makes the mutual benefits of cooperation more tangible. Moreover, equivalent groups will more likely provide an equal level of contribution to a joint enterprise; this is particularly relevant given that collective efficacy (i.e., the perceived ability of the groups to effectively work together) is predictive of cooperation (Klavina & van Zomeren, 2018). The heightened salience of shared goals and collective efficacy makes a cooperative intergroup relationship between equivalent groups an attractive prospect for an agentic fused actor—drawing upon the resources of their in-group as a secure base—to explore and act on.

However, equivalent groups may occasionally arouse a greater level of threat; such groups might represent a challenge to the optimal distinctiveness provided by the in-group (Brewer, 1991) or be viewed as a competitor for resources (Brewer, 1999). Hence, if any of these sources of threat are particularly salient, it may weaken the relationship between fusion and cooperation with an equivalent out-group as indicated by the threat moderator in the model. Nevertheless, fused actors should be particularly well-placed to overcome the potentially increased threat associated with equivalent groups. The emphasis placed on unique individual identities within fused groups may help meet the need for optimal distinctiveness (Swann et al., 2012), reflected in research which found that a personal “need for uniqueness” did not explain changes in the relationship between fusion and willingness to fight and die for the group (Paredes et al., 2018), suggesting that intergroup similarity should represent less of a threat for fused actors. Self-affirmation, which could be regularly engendered by a fused group that celebrates its members’ uniqueness and personal achievements, may further buffer fused actors against the threats associated with equivalent out-groups (Badea & Sherman, 2018; Cohen & Sherman, 2014). Moreover, high personal agency—which is associated with fusion (Besta et al., 2016)—can help fused actors determine when cooperation (such as trading or sharing resources) or conflict is a more appropriate strategy for the context (Boone et al., 2002). This may help fused actors perceive shared intergroup goals and collective efficacy, allowing them to recognize an equivalent group as a potential partner rather than an inevitable competitor. For these reasons, we argue that the usual barriers to cooperation between equivalent groups are likely reduced in the case of fused actors and that our model should still be predictive when applied to equivalent out-groups.

The fusion secure-base hypothesis should also apply to all varieties of in-groups and out-groups, including the hate and extremist groups that have featured prominently in the fusion literature. Of course, given the causal role of threat in most theories of prejudice (e.g., Integrated Threat Theory; Stephan & Stephan, 2000), fusion to a hate group would certainly be unlikely to promote cooperation with the out-group target of the in-group’s prejudice, as predicted by the presence of the threat moderator in the model. The threat moderator likely also accounts for cases when the cause of prejudice is not theoretically dependent on out-group threat, such as when out-group members are dehumanized and seen as subhuman (see Haslam, 2006), as even this tends to be predicted by perceptions of threat (e.g., Esses et al., 2013). Nonetheless, as previously argued, fused actors tend to direct violence toward specific threats (e.g., Newson et al., 2018) and very few antisocial groups are likely to be prejudiced against all out-groups, with many willing to cooperate with out-groups that are ideologically compatible (e.g., Boko Haram and ISIS) or can facilitate a short term goal. Hence, the intergroup context should prove more predictive of whether fused actors are likely to cooperate with an out-group member than the norms or values of the fused group itself.

Finally, it is worth considering the implications of the fusion-secure base hypothesis in terms of fusion’s evolutionary origins. Whitehouse (2018a) has argued that fusion likely evolved via kin selection in response to the selection pressure of intergroup conflict, with fused Paleolithic tribal bands better able to cope with the chronic threat of warfare and out-group raiding. This assertion is supported via mathematical modeling which demonstrated that dysphoric (fitness-decreasing) experiences promoted more in-group cooperation than euphoric (fitness-decreasing) experiences, particularly when simulating intergroup conflicts (see Whitehouse et al., 2017, for a more detailed explanation). The theory further contends that shared dysphoric experiences (e.g., combat, collective rituals, and shared pain) are a pathway to fusion, evoking perceptions of a “shared essence” between group members and instilling the deep sense of devotion to the group needed to survive a conflict. There is empirical support for this contention: Frontline soldiers (i.e., those who directly experience combat) reported higher levels of fusion than those in logistical roles (Whitehouse et al., 2014), fans of losing football teams indicated a higher willingness to self-sacrifice for their teams than fans of winning teams, with the effect mediated by fusion (Whitehouse et al., 2017), manipulating the salience of the 2013 Boston Marathon Bombings increased fusion among Bostonians who experienced high levels of negative affect (Jong et al., 2015), and experiences of combat and ritualized whipping both predicted fusion (Whitehouse et al., 2017). Although others have suggested that a need for intergroup cooperation could have also shaped fusion’s evolution (Wiessner, 2018), it seems apparent that shared dysphoric experiences likely played a role. Nevertheless, collective euphoric experiences are also likely involved in group bonding (Xygalatas, 2014), with new evidence suggesting that fusion can also be elicited by emotions such as awe (Naclerio & Van Cappellen, 2021; Newson et al., 2021) and inspiration (Gómez et al., 2021). This implies that while dysphoric experiences may be a more potent method of eliciting fusion, fusion still exists and can be evoked in relatively safe, nondysphoric situations. Fusion could facilitate in-group and intergroup cooperation in these contexts, both of which still benefit the in-group. Hence, while the existential threat of warfare likely necessitates extraordinarily high levels of fusion to ensure the group’s survival, and may explain its evolutionary origins, the persistent adaptive advantages of a secure base mean that fusion exists and provides value to the group even during periods of peace.

Preliminary Empirical Evidence for the Fusion Secure-Base Hypothesis

There is some preliminary empirical evidence to support the fusion secure-base hypothesis. First, cross-cultural research by Purzycki and Lang (2019) tested whether fusion with a local co-religious, co-ethnic group would come at the cost of poorer out-group relations with nonlocal religious and ethnic out-group members. Fusion was unexpectedly a moderate positive predictor of out-group fusion, leading the authors to argue that fusion may represent a general measure of prosociality. However, this explanation is difficult to square with fusion’s often-violent outcomes and is at odds with past research indicating that fusion to the country does not predict fusion to various other groups, such as friends, family, and religion (Swann et al., 2009). One way of reconciling these results is to note that out-group fusion measures in Purzycki and Lang (2019) were targeted at out-group members rather than the group, whereas in Swann et al. (2009), fusion was directed at the group itself. This suggests, in line with the fusion-secure base hypothesis, that in-group fusion may not predict out-group fusion per se but rather feelings of connection to, or a desire to connect with, out-group members. It is worth noting that in-group fusion was considerably higher than out-group fusion across all samples. This implies that participants still recognized a distinction between in-groups and out-groups, suggesting that the in-group–out-group relationship was not an artifact of reduced group salience but rather the result of a secure base.

A similar study by Kunst et al. (2018) examined how people can fuse with disadvantaged out-groups (e.g., Kurds) when doing so aligns with their political motivations (e.g., a left-wing ideology), although only one of its studies explicitly measured both in-group and out-group fusion. This study surveyed 83 non-Kurdish Leftists from mostly Western countries who aspired to fight with the Kurdish People’s Protection Unit (YPG), a military force responsible for defending Kurdistan from ISIS. The study found that the participants were more likely to feel fused with Kurds, and fight for them, when they felt their political orientation morally compelled them to. More importantly, fusion with the participant’s ethnic in-group was the strongest positive predictor of fusion to Kurds out of all variables tested and was positively correlated with self-reported likelihood to join the YPG. Given that people typically have friendship groups of the same ethnicity (Ramiah et al., 2015), fusion with ethnicity may reflect a more local fusion with people of the same ethnicity. These results could hence imply that fusion with an in-group provided the secure base which in turn empowered participants to explore, connect with, and ultimately fight for out-groups that align with their personal ideology, although the study’s relatively small sample size (N = 83) and focus on a niche subset of left-wingers (i.e., Westerners interested in fighting ISIS) limit the generalizability of these findings. It should be emphasized that the research conducted by Purzycki and Lang (2019) and Kunst et al. (2018) represents only preliminary evidence in favor of the fusion secure-base hypothesis, with the majority of the model’s evidence residing in the strong empirical link between a secure base schema and an increased willingness to interact with and trust out-group members, and the clear suitability of a fused group to act as a secure base.

Initial studies have examined the fusion-secure base hypothesis, with a particular focus on the relationship between identity fusion, in-group trust, and out-group trust (Klein, Greenaway, & Bastian, 2022). Several online studies have been run using U.K. and U.S. samples, largely focused on fusion to a participant’s most important group (excluding family). These tend to be friendship or workgroups, thus avoiding the issue of targeting unusual or extremist groups that may be less likely to interact with out-groups. Results from cross-sectional studies have shown that identity fusion is positively correlated with general trust and a willingness to trust and interact with out-group members, even controlling for key affiliative personality variables such as agreeableness. A subsequent longitudinal study examined fusion in English Premier League (EPL) fans (N = 266) before and after the decision of several EPL teams to join a European Super League (ESL). The ESL was universally panned and led to subsequent supporter protests, which triggered an eventual decision by the EPL teams involved to renege on the ESL deal (Panja, 2021). The study found that a positive increase in fusion following the successful protests predicted increases in general trust, and this relationship was mediated by increased in-group trust. These results provide initial direct evidence for the fusion secure-base hypothesis, although if future research fails to replicate these findings then the model may need to be revised or discarded.

A very small number of studies have examined fusion and out-group prosociality and failed to find a positive relationship. However, these studies were designed to observe parochialism rather than intergroup cooperation and, while they found evidence that fused actors tend to prioritize the in-group over out-groups, the zero-sum or adversarial study frameworks mean that their results do not undermine the fusion secure-base hypothesis. For instance, Swann, Gomez, Dovidio, et al. (2010) found that fusion to Spain predicted sacrificially jumping in front of a trolley car to save fellow Spaniards and Europeans (an extended in-group) but not Americans (out-group). Nevertheless, the experiment required participants to choose between doing nothing, saving five Europeans, or saving five Americans, thus only indicating that fused actors prioritize the in-group over the out-group. In any case, as previously argued, the fusion secure-base hypothesis does not predict prosociality per se, and a fused actor would likely only sacrifice themselves for an out-group member if the in-group stood to benefit (e.g., via reciprocal sacrifices or support) or if it was in line with the ideology or norms of the in-group (e.g., a fused police officer sacrificing themselves for a civilian). Similarly, Apps et al. (2018) found that fused people were less likely to accept a fair offer in a game of Ultimatum from supporters of a rival football team than members of the in-group. However, there was no statistical difference in their rate of accepting fair offers from the in-group or a neutral person (i.e., not a member of a rival out-group), indicating that fusion only reduces cooperation when an antagonistic relationship with an out-group has already been established.

Future Directions

The present article has outlined the case for identity fusion having a potentially positive influence on intergroup cooperation. Intergroup cooperation and warfare have both shaped human social evolution (Majolo, 2019), so it is worthwhile to consider the role of identity fusion in both contexts. The fusion secure-base hypothesis does so by drawing from multiple bodies of literature to explain how fusion can both promote cooperation in times of peace and yet still drive aggression when the group is threatened. While initial empirical results are promising, there have been few studies explicitly designed to test the model and research should continue to establish the link between identity fusion, a secure base schema, and out-group trust and cooperation. Specifically, future research should test the hypothesis that fusion predicts intergroup exploration and, in the absence of out-group threat, intergroup cooperation. There are likely moderators other than the threat which may strengthen or weaken the basic relationship between fusion and out-group cooperation, as discussed subsequently, but the tendency for the threat to “flick the switch” between violence and cooperation is a core prediction of the model. If fusion was found not to be predictive of a willingness to explore relationships with out-groups and engage in mutually beneficial intergroup cooperation, or if threat was found not to moderate this relationship, then the model would have to be substantially revised or abandoned. A theoretical setback would be if the model proved only predictive among certain intergroup relationships, such as between groups that are on different levels of abstraction (e.g., fusion to a friendship group predicted cooperation with a workgroup or sports team, but not another group of friends). Although the likely explanation for this (i.e., out-group threat) is captured in the model, it would make the theory overall less compelling and useful. While there are theoretical reasons to believe the model does apply to related and relevant out-groups (e.g., similar goals, heightened collective efficacy), empirical research directed specifically at intergroup relationships between equivalent groups would help address this concern.

Further elucidation of the model and its components can be undertaken by identifying relevant moderators of each pathway. One potential candidate is the dispositional attachment style of the fused actors themselves and whether an insecure attachment style (i.e., attachment anxiety or avoidance) affects their capacity for fusion and intergroup cooperation. Although avoidance, which is marked by difficulty trusting or becoming close to others, is very unlikely to be conducive to fusion, persons with an anxious attachment style tend to express an overwhelming desire for closeness (Hazan & Shaver, 1987). Given this strong desire to merge with others, anxiously attached persons may be prone to fusion and particularly willing to fight and die for the group, thereby hypothetically resembling—at least superficially—fused actors. However, it is unclear whether anxiously-attached people fuse in the way that fusion is typically conceptualized. Fusion is positioned as a synergistic combination of the personal and social selves, in which each takes equal prominence, and marked by a high level of perceived agency over the group (Swann et al., 2012). Considering attachment anxiety is characterized by feelings of unworthiness and fear of abandonment (Hazan & Shaver, 1987; Smith et al., 1999), this is unlikely to manifest in an endorsement of items in the fusion scale that reflect confidence in the self (e.g., “I make my group strong”) or in any items from the agency scale (e.g., “I am able to control what my group does”). An inability to successfully bond with groups is reflected in empirical research; anxious-attachment and avoidance group attachment both negatively predicted group identification, warmth toward the group, and an ability to problem-solve with the group, with attachment-anxiety predicting a warmth reduction 9 weeks later (Smith et al., 1999). Further research has found that anxiously-attached people were less likely to identify with and seek support from their in-group in response to an interpersonal threat, particularly in the case of intimate in-groups (Crisp et al., 2009), and that securely attached people report higher levels of communal identification (a type of identification that is conceptually similar to fusion) than those with insecure attachment styles (Milanov et al., 2013). Hence, there are probably qualitative differences in the way securely and anxiously-attached people fuse to groups, with perceptions of a secure base likely weaker among the latter.

A further moderator is the degree to which the fused group supports each member’s autonomous goal pursuit. Certain groups, despite successfully instilling a sense of felt security, may implicitly or explicitly suppress group members’ attempts to challenge prevailing group values or customs (e.g., a terrorist prohibited from questioning the group’s ideology). This is somewhat captured by the concept of tight and loose cultures, in which tight cultures have strong norms and a low tolerance for deviance and loose cultures have the reverse (Gelfand et al., 2011). Of course, practically all groups place some limit on individual expression, but if a group is considered overly intrusive (i.e., high cultural tightness) then it may cause a fused actor to feel misunderstood or invalidated. If these feelings are sustained, then defusion (i.e., the reversal of the fusion process) may eventually ensue and the group will cease to represent a secure base. Defusion has been discussed in the fusion literature (Fredman et al., 2015), with correlational (Vázquez et al., 2017) and experimental (Gómez et al., 2019) evidence supporting its viability, particularly in response to perceptions of group betrayal (i.e., behaviors that undermine a secure base schema). The irrevocability principle indicates, however, that defusion is difficult and it is possible to imagine someone remaining fused to a group that is manipulative and controlling, particularly if the fused actor is in denial or oblivious to the suppressive nature of the group. In these situations, although the group may still provide a safe-haven function (i.e., physical protection), the secure-base function may be diminished. This will likely reduce the extent to which a fused actor feels empowered to interact and cooperate with out-group members. Hence, while the model stipulates that identity fusion predicts intergroup exploration, this relationship could be moderated by the tightness of the group. Indeed, cultural tightness have been found to be more wary of outside influences and less willing to interact with outsiders (Gelfand et al., 2011), suggesting a relative weakness of the secure-base function in tight groups. Future research could investigate the relative importance of each function (i.e., secure-base and safe-haven), and whether both mediational paths are equally predictive of intergroup exploration and cooperation.

There are other theoretical questions that are also worth answering. For instance, are local and extended fusion equally likely to provide a secure base? The validity of extended fusion as a motivator of extreme sacrifice has been questioned (Whitehouse, 2018a), so it is reasonable to question it as a driver of intergroup cooperation too. Local fusion may provide a more potent secure-base function, owing to strong familial bonds reinforced by actual day-to-day contact, although given there is evidence that extended fusion is borne from the projection of local interpersonal ties (Vázquez et al., 2015), this may be common to both forms of fusion. By contrast, extended fusion often implies the presence of a more powerful and larger group (e.g., a nation), which may increase perceptions of in-group formidability that feed into the safe-haven function. Future research will be needed to compare local and extended fusion as distinct sources of a secure base. It would be similarly instructive to further elucidate the role of threat in the theory when it is not explicitly associated with an out-group. Although general dysphoria increases self-sacrificial behavior for the group via fusion (Whitehouse et al., 2017), and has been proposed as a cause of fusion itself (Whitehouse, 2018a), it is not clear what implications it has for intergroup relations. For example, a resource threat (e.g., a drought) could make fused actors less likely to cooperate with out-groups (due to the higher consequences of nonreciprocation) or more likely (due to a greater need to trade and harvest resources). Social identity theory research has found that the decision to cooperate with out-groups is largely driven by perceptions of whether cooperation is in the best interests of both groups (Montoya & Pittinsky, 2011) and whether both groups can work together (Klavina & van Zomeren, 2018), suggesting that fused actors will similarly be guided by the idiosyncratic nature of the threat and intergroup relationship in question. Given that persons high in personal agency are faster at learning whether cooperation or defection is the most appropriate strategy than those low in agency (Boone et al., 2002), fused actors may be particularly adept at deciding whether to cooperate in response to changing threat levels.

Due to the relative dearth of studies explicitly addressing the topic of fusion and out-group cooperation, it is also difficult to know how far a fused person would go to assist an out-group and under what circumstances. For instance, Crimston and Hornsey (2018) suggest that people often self-sacrifice for out-group members, as demonstrated by White activists who participated in the U.S. civil rights movement. Although they offered moral expansiveness as an explanation, it is certainly not the only motivator of out-group self-sacrifice (Gómez et al., 2020). Groups have long formed coalitions in times of dysphoria, particularly warfare. A fused actor could conceivably fight and die for an allied out-group, compelled by a desire to defeat a common enemy (e.g., Klavina & van Zomeren, 2018) or abide by their ideological convictions (e.g., Kunst et al., 2018). History is littered with relevant examples, such as the immeasurable sacrifices made by British soldiers assisting France and Belgium in World War I. Coalitions can blur the line between in-group and out-group, causing fused actors to think of themselves as fighting and dying for an extended in-group (Whitehouse, 2018b). For example, Swann, Gomez, Dovidio, et al. (2010) found that Spaniards were willing to sacrifice themselves for Europeans, which the authors suggested may have reflected a sense of solidarity against recent terrorist threats in Europe. The common in-group identity model argues that in cooperative intergroup relationships recategorization may occur, causing members of multiple groups to conceive of themselves as part of a single superordinate group (Gaertner & Dovidio, 2000). This makes it difficult to establish if the primary in-group retains a privileged status or is meaningfully distinct from the out-group at all.

Research into understanding when and how fused actors from distinctive groups can fuse to an extended superordinate group would work to address these concerns. There is some evidence that local fusion to one group can predict extended fusion to another group, at least when the groups are nested within one another. For example, Vázquez et al. (2015) found that fusion to sibling predicted fusion to Spain, highlighting the projection of relational ties from a local group onto an extended in-group. However, this does not address the question of how fused actors from equivalent groups (e.g., Spain and England) come to conceive of themselves as fused to a superordinate group (e.g., Europe) or what level of group abstraction retains the most devotion. Optimal distinctiveness theory suggests that a need for distinctiveness tends to break superordinate groups into subgroups over time (Brewer, 1991), while more recent iterations of the common in-group identity model have emphasized the idea of dual identity in which people still conceive of different groups as separate entities even within the same superordinate group (Dovidio et al., 2010). This suggests that even in particularly cohesive intergroup relationships fused actors likely still recognize and prioritize the in-group and that any detection of out-group threat may abruptly split the superordinate group back into its original subgroups. Moreover, fused actors may be less likely than unfused persons to recategorize and endorse a superordinate group. Swann et al. (2012) argue that the all-consuming nature of fusion may inhibit fused actors from displaying the role flexibility needed to establish deep relationships with persons outside the group. This suggests that even in instances of intergroup cooperation, fused actors may be particularly unlikely to project the familial bonds onto out-group members necessary to engender intergroup fusion. In any case, intergroup fusion is unlikely to develop spontaneously, with intergroup contact theory (see Brown & Hewstone, 2005) suggesting that strong intergroup relationships are generally a result of continued positive contact (Pettigrew & Tropp, 2006). Hence, while the fusion secure-base hypothesis offers a mechanism through which intergroup interactions might be initiated, more established pathways to fusion, such as shared experiences (Whitehouse et al., 2017), likely better explain how intergroup relational ties develop. The potential causal relationship between the fusion secure-base hypothesis and intergroup fusion is an interesting concept and warrants further investigation.

The fusion secure-base hypothesis—through uniting the fusion and attachment literature—also sets up a novel framework for understanding fusion. For instance, it is worth exploring whether many of the positive outcomes of a secure base, including those that are not directly related to intergroup relations, like improved emotional regulation and better coping under stress (Sroufe et al., 2005), are predicted by fusion. These may in turn predict other correlates of fusion, such as perceptions of invulnerability in the face of out-group hostility (Gomez, Brooks, et al., 2011), thereby shedding light on the precise psychological processes involved in fighting and dying for the group. On a related note, it would be enlightening to investigate whether fusion can “repair” insecure attachment styles, as healthy romantic relationships can (Arriaga et al., 2013; Simpson et al., 2003; Stanton et al., 2017). Mikulincer and Shaver (2017) proposed that a supportive and cohesive group should have the power to beneficially alter a person’s attachment style and psychological functioning; in the context of the fusion secure-base hypothesis, it is difficult to consider a more suitable candidate than that of a fused group. A secure group attachment style may engender a working model of groups as warm, trustworthy, and accepting (Smith et al., 1999), thereby offering another path to intergroup cooperation.

Conclusion

The fusion secure-base hypothesis argues that a fused group can act as a secure base, tending to facilitate rather than undermine cooperative intergroup relationships. The hypothesis is underlined by the key characteristics of identity fusion, all of which combine to produce a group that is perceived as a reliable source of protection, support, and comfort. The ensuing secure base schema allows fused actors to more easily trust and cooperate with others, thereby facilitating the establishment of reciprocal relationships with nonthreatening out-groups. Nevertheless, if circumstances change and the intergroup relationship turns antagonistic then intergroup trust will evaporate, and fused actors will become motivated to inflict whatever extreme acts of violence are necessary to ensure their in-group’s survival.