Why do multiparty cabinets in parliamentary democracies produce more extreme foreign policies than single-party cabinets? Our paper argues that particular institutional and psychological dynamics are responsible for extremity. We test this argument using a global events dataset incorporating foreign policy behaviors of numerous multiparty and single-party governments. We find that more parties and weak parliaments promote extremity in coalitions, but parliamentary strength has the opposite effect for single-party governments. This study challenges existing expectations about the impact of democratic institutions on foreign policy.