Exploring the origins of identity fusion: Shared emotional experience activates fusion with the group over time

Abstract Identity fusion is a visceral feeling of oneness with a group, known to strongly motivate extreme pro‐group behaviour. However, the evidence on its causes is currently limited, primarily due to the prevalence of cross‐sectional research. To address this gap, this study analysed the evolution of fusion in response to a massive collective ritual, Korrika —a race in support of the Basque language—, over three time periods: before ( n = 748) and immediately following participation ( n = 402), and 7 weeks thereafter ( n = 273). Furthermore, we explored the potential mediating roles of two key factors: perceived emotional synchrony, a sense of emotional unity among participants that emerges during collective rituals, and kama muta (moved by love), an unexplored emotion in relation to fusion, which arises from feelings of shared essence. The proportion of fused participants increased significantly after participation and remained stable for at least 7 weeks. Perceived emotional synchrony and kama muta apparently explained the effect of participants' behavioural involvement in the ritual on subsequent fusion, but only among those who were not previously fused with Korrika participants. We conclude that emotional processes during collective rituals play a fundamental role in the construction of identity fusion.