Even though international conflicts often lead to varied responses from state actors, the reasons behind these differences remain underexplored, especially regarding political support for those who are harmed. This study investigates why some states express solidarity with those harmed in armed conflict, focusing on the Israel-Gaza conflict as a case study. I argue that the intensity of civil society advocacy significantly influences state actors’ solidarity behaviour. This argument is structured around a three-step causal mechanism: civil society advocacy raises public awareness, prompting public pressure on state actors, which increases costs of inaction, leading to solidarity expressions. By employing a structured, focused comparison of Spain and Italy, the study qualitatively assesses public solidarity manifestations and civil society advocacy intensity, using protest data and media coverage as indicators. The findings suggest that Spain’s intense civil society advocacy has resulted in significant public pressure and official solidarity displays, whereas Italy’s weaker civil society response led to less solidarity manifestations. These results highlight the crucial role of civil society in shaping state behaviour during conflicts, providing both theoretical and empirical contributions to the study of civic engagement and state’s conflict response.