ABSTRACT: This study aims to reassess the position of the Roman Catholic Church regarding the Serbian Orthodox population in the period leading up to the establishment of the Independent State of Croatia. Due to the broad chronological and geographical scope of the topic, the analysis is focused on micro case studies, including the question of religious “communion” the role of Catholic clergy in the Croatian national movement, the Concordat between Yugoslavia and the Vatican, and Catholic Action. By examining these focal points, the study seeks to explore the cultural, political, and ideological dynamics of the Catholic Church’s relationship with the Serbian Orthodox population. Furthermore, the research highlights certain continuities in this relationship, culminating in the persecution, oppression, and genocide of the Serbian people during the existence of the Independent State of Croatia.

KEYWORDS: Roman Catholic Church, Serbian Orthodox, church communion, Croatia, Slavonia, catholic clergy, Concordat, Catholic action

SUMMARY: This article reexamines the Holy See’s evolving approach to the Serbian Orthodox population in the Balkans from the Counter-Reformation through the interwar period, highlighting how religious policy became increasingly entangled with emerging national ideologies. Initially focused on bringing Orthodox Christians into communion with Rome, the Roman Catholic Church’s efforts intensified in the 19th century. Following the dissolution of Austria-Hungary and the creation of the Kingdom of Serbs, Croats, and Slovenes, the Holy See faced a transformed political and religious land scape characterized by the absence of existing concordat agreements and heightened tensions over interconfessional balance and church–state relations. The failed Concordat negotiations with Yugoslavia not only exposed deep confessional rifts but also reinforced Catholic perceptions of marginalization, fueling nationalist sentiments. The mobilization of Catholic lay organizations further politicized religious identity, aligning Church interests with Croatian nationalist goals. By the late 1930s, the unresolved tensions between the Holy See and the Yugoslav state manifested through stalled diplomacy, failed integration, and rising mistrust, contributed to the ideological conditions that enabled the later radicalization under the Ustasha regime.