by Cormac Auty – OICD Intern

As part of The Power of Identity’s Theory Corner, we summarize this useful theoretical framework, one which can give us insights into the intricate dynamics of social cohesion in small groups and why some will resort to violence.

This Theory Corner piece was inspired by Steve Medeiros, Associate Director at the William Joiner Institute for The Study of War and Social Consequences at the University of Massachusetts, Boston, who gave a lecture to the OICD’s internship program on Identity Fusion Theory. Steve is currently working with US soldiers to investigate processes of Identity Fusion in this under-explored context.

Introduction to Identity Fusion Theory
Identity Fusion Theory emerged as a theoretical concept in the aftermath of 9/11 and the Madrid Train Bombings, as social scientists grappled with a significant increase in global terrorism (Gómez et al. 2020). In 2009, the first empirical work on the concept was published (see Swann, Gómez, Seyle, Morales, & Huici, 2009). This represented the first theoretical investigation into the link between extreme behaviour and the observed endurance of people’s personal identities in processes of group alignment (Swann et al. 2009).

Key Principles of Identity Fusion Theory
Identity Fusion is, at its core, a profound feeling of ‘oneness’ and belonging to a group, to which individual members are so strongly bonded, or ‘fused’ that they would be willing to engage in extreme behaviors for that group and to the detriment of themselves (Whitehouse 2018).

Four key principles constitute Identity Fusion. These are:
1. The agentic-personal-self principle: individual members of a group will display a high level of agency which serves the needs of the group.
2. The identity synergy principle: personal and social identities can together direct a person’s behaviour with regard to their group, since both identities can be simultaneously active.
3. The relational ties principle: individual group members are aware of and respect the personal identities of their fellow members.
4. The irrevocability principle: Identity Fusion is persistent.
(Swann et al. 2009, Gómez et al. 2020)

In his presentation to the OICD, Steve Medeiros touched on the cultural, cognitive, evolutionary and biological underpinnings and mechanisms that contribute to extreme fused identity structures. He stressed that when we talk about Identity Fusion we are talking about extreme cooperation as well as extreme violence and highlighted the evolutionary explanation for fusion; highly fused groups were likely to outperform weakly fused groups in our ancestral past.

Identity Fusion vs. Social Identity Theory
Identity Fusion Theory has been positioned by its proponents as distinct from Social Identity Theory, itself introduced by Henri Tajfel and John Turner in the 1970s and 1980s. Proponents of Fusion Theory have pushed back against common misconceptions which view it as simply ‘super-identification’, as in the application of Social Identity Theory in the context of extreme pro-group behaviour (Gómez et al. 2020). Identity Fusion has thus far been presented as one variation of groups alignment displayed by individuals (Vázquez et al. 2023). In fact, identification as outlined by Social Identity Theory and fusion can be independent measurable variables. Swann and Buhrmester (2015) have suggested that individuals could be highly identified with a group, yet weakly fused with it. The authors have questioned whether a highly identified, yet weakly fused individual, may, due to a lack of relational ties to other group members, be prepared to endorse the sacrifice of fellow members for the good of the collective (Swann and Buhrmester 2015).

Studies have sought to prove the distinction between Social Identity Theory and Identity Fusion Theory. It has been found that terrorists do not suffer from weak personal identities, as would be predicted by Social Identity Theory (Swann et al. 2009). These individuals do not become faceless actors working solely for what they perceive as the good of their collective (Swann et al. 2009). Importantly, Social Identity Theory relies on there being a process of depersonalisation at play in the wider identification process (Swann et al. 2009). Fusion Theory, on the other hand, does not rely on this process of depersonalisation and instead assumes that the social and personal identities of fused individuals reinforce each other rather than existing in an inverse relationship – the identity synergy principle (Swann et al. 2009).

Promising Developments in Identity Fusion Research
Many multidisciplinary studies across the world have demonstrated Identity Fusion Theory’s ability to predict willingness for fighting and dying for one’s group and its theorists have highlighted significant interest in the theory from across the social sciences, as well as from governments (Gómez et al. 2020). The period since 2015 in particular, has seen a substantial increase in the number of empirical and theoretical contributions to the theory, investigating case studies involving shared biological links and shared experiences in groups without familial ties between members (Gómez et al. 2020).

Some recent research has sought to explore more positive contexts in which identity fusion occurs. Fused individuals are more prepared to carry out ‘intense sacrifices for the group’, but studies are showing that the context helps determine whether these sacrifices will present themselves in violent or prosocial ways (Gómez et al. 2020). Steve Medeiros argued in his presentation that attention also needs to be paid to group values in determining the outcome of a particular fusion process, which might be positive for the group or involve the degradation of an out-group.

Along these lines, a 2023 paper on Identity Fusion explored whether it could foster social harmony. This study found that strongly fused participants expressed ‘more positive sentiments towards familiar out-group members than weakly fused participants’ (Vázquez et al. 2023). Individuals who are strongly fused to their own group, appear to feel less threatened by contact with familiar outgroups, since they have their own secure, fused base (Vázquez et al. 2023). In fact, if a strongly fused individual is threatened by an outgroup, a violent response was found to only be preferred when such violence can be morally justified, with the default response being non-violence (Vázquez et al. 2023). Hostility, at least of a non-violent kind however, is to be expected following a perceived threat from an out-group. In cases where there is no negative contact between groups, Identity Fusion was positively correlated with warmer feelings being shown to members of the other group (Vázquez et al. 2023).

One of the fundamental parts of Identity Fusion Theory is the idea that the personal identity and social identity of an individual exist together in a mutually reinforcing relationship. The theory, in other words, recognizes the role of the personal self in explaining individuals’ ties to other group members. Individuals are, in Fusion Theory, understood as distinct and unique actors who also have relational ties to other members of a group to which they are fused. This focus on intra-group dynamics demonstrates a rather nuanced development from classic Social Identity Theory.

Reducing Fusion and Countering Violent Extremism

Although one of its principles is irrevocability, researchers connected to the theory have, in recent years, begun to look more at the prospect of a reduction in fusion (Gómez et al. 2020). Findings here could be utilized in addressing violent radicalization (Gómez et al. 2020). Recent studies have investigated the degradation of collective ties or relational ties and the consequences of these actions on demonstrations of pro-group behaviour (Gómez et al. 2020). These investigations have found that weakening these ties does indeed lead to a ‘diminished fusion’ with the group (Gómez et al. 2020).

In conjunction with these investigations, a 2022 paper by Ebner et al. explored Fusion Theory’s utility to counter-terrorism work. Their study recognized that ‘strong group identification often occurs in tandem with high levels of Identity Fusion’, but it found that the presence of fusion and importantly fusion under threat is a noticeably stronger predictor of extremist acts of violence than identification is (Ebner et al. 2022). The authors of this study have made a departure from the pictorial or verbal questionnaire method of measuring fusion favored in the past. Through a linguistic analysis of published extremist manifestos, they have started the development of theory-led diagnostic tools for early violence prevention and one which the authors hope to refine in cooperation with counter-terrorism professionals (Ebner et al. 2022).

OICD’s Interpretation and Application
OICD Executive Director, Bruce White, highlights Identity Fusion Theory’s utility in helping practitioners see how identity-based divisions and classifications can be mapped onto geographic and interactive contexts.

Seeing Identity Fusion’s contribution to the concept of ‘agency’ as particularly unique, Bruce comments: “We at the OICD have not traditionally looked at how agency operates WITHIN a context of a single, locked identity pathways, such as during radicalization towards extreme violence. In incorporating this theoretical approach, we see that, as in other ways, the locked or single identity provides solutions and fulfils needs. Actions taken within these single identities might be seen as providing the sense that the individual is operating from a position of agency, even though there are no other identity choices, and perhaps therefore that this ‘sense of agency’ might be best viewed as a kind of ‘false agency’”.

“On a more technical level, the actions taken reenforce membership which feels good if belonging is a core need driving inclusion. There may therefore be a theoretical bridge between fusion and our idea of fixed identities or identity stasis. The ‘identity pathology’ as we see it at the OICD is that options for identification are removed, and ‘real agency’ DECREASED as someone moves further towards identity stasis and violent acts. We look forward to continuing to investigate this intersection of identity and agency theory moving forward.”


Ebner, J., Rapp, C., & Rust, H. (2022). Is there a language of terrorists? A comparative manifesto analysis. Studies in Conflict & Terrorism, 1-26.

Gómez, A., Brooks, M. L., Buhrmester, M. D., Vázquez, A., Jetten, J., & Swann, W. B. (2011). On the nature of identity fusion: Insights into the construct and a new measure. Journal of Personality and Social Psychology, 100(5), 918–933.

Gómez, Á., Chinchilla, J., Vázquez, A., López-Rodríguez, L., Paredes, B., & Martínez, M. (2020). Recent advances, misconceptions, untested assumptions, and future research agenda for identity fusion theory. Social and Personality Psychology Compass, 14(6).

Swann, W. B., Gómez, Á., Seyle, D. C., Morales, J. F., & Huici, C. (2009). Identity fusion: The interplay of personal and social identities in extreme group behavior. Journal of Personality and Social Psychology, 96(5), 995–1011.

Swann, W. B., Jetten, J., Gómez, Á., Whitehouse, H., & Bastian, B. (2012). When group membership gets personal: A theory of identity fusion. Psychological Review, 119(3), 441–456.

Swann, W. B., Buhrmester, M. D., Gómez, Á., Jetten, J., Bastian, B., Vázquez, A., Ariyanto, A., Besta, T., Christ, O., Cui, L., Finchilescu, G., González, R., Goto, N., Hornsey, M., Sharma, S., Susianto, H., & Zhang, A. (2014). What makes a group worth dying for? Identity fusion fosters perception of familial ties, promoting self-sacrifice. Journal of Personality and Social Psychology, 106(6), 912–926.

Vázquez, A., Gómez, Á., Ordoñana, J. R., Swann, W. B., & Whitehouse, H. (2017). Sharing genes fosters identity fusion and altruism. Self and Identity, 16(6), 684-702.

Vázquez, A., Stenseng, F., Ric, F., Feddes, R., Martinussen, M., & Gómez, Á. (2023). Can identity fusion foster social harmony? Strongly fused individuals embrace familiar outgroup members unless threatened. Journal of Experimental Social Psychology, 107, 104462.

Whitehouse, H. (2018). Dying for the group: Towards a general theory of extreme self-sacrifice. Behavioral and Brain Sciences, 41, e192.

Whitehouse, H., McQuinn, B., Buhrmester, M., & Swann, W. B. (2014). Brothers in arms: Libyan revolutionaries bond like family. Proceedings of the National Academy of Sciences, 111(50), 17783–17785.