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

Abstract

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.