Countries involved in conflicts learn about their military strength from the battlefield. We study how a third party intervenes to manipulate this learning. An attacker and a defender engage in a conflict whose outcome conveys information about the attacker's strength. A third party fears the attacker’s aggressiveness and can intervene to help the defender. This intervention is risky: if the attacker wins despite the help the defender receives, its aggressiveness increases even further. We show that optimal third-party intervention is non-monotonic in the attacker’s strength. We also show that patriotism is a defensive strategy for the defender because boosting the resolve to fight forces third-party intervention.

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