When studying religion in war and conflicts, the focus is mostly either on its potential to escalate or to pacify the situation. However, the role of religion during war at the international and transnational levels has so far been neglected, even though religion is represented in international organisations. The Ukraine War has seen strongly diverging roles of religions since Russia first launched attacks on 24 February 2022. While Patriarch Kirill, head of the Russian Orthodox Church, presented the Russian National Guard with an icon to inspire young soldiers when defending their fatherland, Pope Francis, head of the Roman Catholic Church criticized the United Nations as being impotent in the Ukraine War. These two examples alone indicate the diverging stances religion can assume in the face of war, ranging from legitimizing acts of aggression to appealing to the international community to re-visit questions of responsibility and the ability to act. In other words, these examples reveal that religion can both strengthen as well as weaken the international order and institutions such as international law, diplomacy, or sovereignty. The first aim is to collect empirical data as to how (transnational) religious actors position themselves at the outbreak and during the course of war in a selection of cases. The second aim is to theorize on the role of religion in international, transnational, and world society, thereby further developing English School approaches to the evolution of institutions.