["European Journal of Social Psychology, EarlyView. ", "\nABSTRACT\nPublic opinion plays a central role in shaping conflict dynamics and influencing wartime policy. In this work, we examined which psychological intergroup interventions could increase public opposition to war. Building on research showing that instrumental reasoning and social identification are central, though not exhaustive, predictors of war‐related attitudes, we designed seven theoretically grounded, social media‐based interventions and tested their effectiveness in an intervention tournament conducted during the January 2025 ceasefire in the Israel–Gaza war, with a sample of Jewish Israelis (N = 1237). One intervention—emphasizing Israel's potential losses if the war continued (achievements‐driven loss aversion)—increased support for ending the war across participants. A second intervention—grouping Jewish Israelis by war‐related attitudes rather than political identification (attitude‐based recategorization)—was effective primarily among left‐leaning participants. These findings demonstrate that carefully designed brief message‐based interventions can influence public opinion and promote de‐escalation, even amid violent conflict.\n"]