Because people have many identities, or multiple identities, social context and cues are important in determining when a social identity or group membership drives behaviour. Traumatic reminders, or triggers, can make group memberships salient. These reminders can take the form of discrete events or even wider events where political or historical context is seen to be relevant. Trauma has the capacity to reveal differences between us, or between us and ‘them’. A long tradition of research in social psychology documents the role of a sense of ingroup and outgroup, ‘us’ and ‘them’, that underlies tensions and hostilities between groups. In contexts where the situation is already oppositional or polarised, these tensions can quickly give rise to anger and even open hostilities. This can lead to a downward spiral of events where the anger and distress associated with traumatic circumstances give rise to social and political action.

This chapter draws out the implications of the patterned nature of traumatic experiences. The chapter offers a new way of understanding trauma that emphasises the significance of group memberships. Trauma and adverse experience can lead to the categorisation and recategorisation of people into different groups, such as labelling them as ‘refugees’ or ‘widows’ due to war or bereavement. Trauma can also reinforce existing group memberships and boundaries. This social identity approach is useful to studying trauma, then, because the risk and experience of trauma can shape identity. And though shared group memberships and identities can be crucial social and psychological resources for coping with trauma, where blame is laid for the experience of a trauma, this can disconnect those who experience trauma from their own group. The chapter emphasises the value of a social psychological analysis, and especially a social identity analysis, in comprehending the relationship between traumatic experiences and our sense of ourselves and others as group members. This hinges on the core idea that group memberships play a crucial role in how we experience and manage trauma.