Does External Threat Unify or Divide? Revisiting the Rally-Round-the-Flag Effect Through Social Cohesion

Liberal democracies face a growing number of violent conflicts, raising the question of whether external threats strengthen social cohesion. While classical sociological theory and public opinion research on the "rally-round-the-flag" effect suggest that external threats unify societies around national identity and leadership, empirical findings remain mixed and rally events are often conditional and short-lived. Crucially, existing studies rarely examine social cohesion itself, focusing instead on approval ratings or affective polarization. This paper addresses that gap by using an Unexpected Event During Survey Design to assess the causal effect of Russia's 2022 full-scale invasion of Ukraine on perceptions of social cohesion in the UK and Germany. Comparing perceived intergroup tensions (e.g., rich–poor, old–young, men–women) before and after the invasion, and tracking effects over several subsequent weeks, the analysis finds that cohesion perceptions remained largely stable. This suggests that even salient external threats do not necessarily override existing societal tensions, challenging core assumptions of the rally-round-the-flag literature.