How Opposing Ideological Groups use Online Interactions to Justify and Mobilise Collective Action

The purpose of this pre-registered study was to investigate how different ideological groups justified and mobilised collective action online. We collected 6878 posts from the social media accounts of pro-Black Lives Matter (n = 13) and anti-Black Lives Matter (n = 9) groups who promoted collective action in the month after George Floyd's murder and the Black Lives Matter (BLM) protests and counter-protests. We used content analysis and natural language processing (NLP) to analyse the content and psychological function of the posts. We found that both groups perceived their action as ‘system-challenging’, with pro-BLM accounts focused more on outgroup actions to mobilise collective action, and anti-BLM accounts focused more on ingroup identity. The reverse pattern occurred when the accounts were attempting to justify action. The implications are that groups’ ideology and socio-structural position should be accounted for when understanding differences in how and why groups mobilise through online interactions.