Treaty obligations and support for collective defence: Evidence from Italy after the invasion of Ukraine

Whether countries and their publics are responsive to the international legal commitments they make is the source of long-standing academic debate. Russia's February 2022 invasion of Ukraine brought real-world significance to these debates. While Ukraine is not a member of the North Atlantic Treaty Organization (NATO), the invasion raised the prospect that other NATO members could be targeted and that Article 5 collective security commitments would be invoked. While recent research suggests that emphasizing mutual defence treaties can increase public support for defending an ally, prior work focuses on US opinion in a less fraught political environment. We constructed and fielded a survey experiment in Italy in the initial weeks of the Ukraine invasion to probe support for defending a NATO ally, the relevance of the Article 5 legal commitment on support for defending an ally, and the potential moderating influence of gender and political party. Our findings show that the Article 5 commitment significantly increased support for defending an ally. Consistent with past research, we find a significant gender gap, with men being more supportive of defending an ally than women; however, both men and women responded to the Article 5 commitment to virtually the same degree. The estimated treatment effect was larger for supporters of right-wing parties than for the left; however, the difference was not statistically significant.