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 or weaken social cohesion. While classical sociological conflict theory and 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 UESD approach paired with Difference-in-Differences (DiD) analyses 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 solidarity, ethnic diversity attitudes, and perceived intergroup tensions (e.g., rich–poor, old–young, men–women) before and after the invasion, the analysis finds that social cohesion remained mostly untouched from the invasion. More compellingly, significant heterogeneous treatment effects between the two countries are identified. The results suggests that even salient external threats do not necessarily override existing societal tensions, and that rally events do not occur universally to the same trigger.