After World War I, Europe faced unstable international relations fueled partly by religious tensions. As Archbishop of the Church of Sweden, Söderblom advanced the ecumenical movement, leading the 1925 Stockholm World Conference of Churches. He stressed that “peace is built not only by treaties but in the minds of people,” urging churches to foster mutual understanding rather than nationalism. This helped spread a new sense of cross-border solidarity within Christianity and complemented the League of Nations’ cooperative diplomacy. His activities later influenced the formation of the World Council of Churches (WCC) and the value system of the United Nations.

Söderblom, a historian of theology, studied post-Reformation confessional splits and proposed a dialogue model based on shared theological cores. At the 1925 Stockholm conference he chose “Life and Work” as the theme, linking practical social issues—labour conditions, disarmament, minority rights—to theological debate. He advocated “functional consensus,” enabling cooperation while preserving denominational identities, and collaborated with governments and the League of Nations to promote peace-education programs. His expansion of ecumenism from doctrinal talks to international relations and social ethics was pioneering, and his ideas were inherited by the post-war “Moral Disarmament” movement.

Drawing on liturgical history and comparative religion, Söderblom developed a cross-confessional ecumenical heuristics as a methodology for inter-denominational negotiations. After the 1925 conference, he used the Organisation for Promoting Christian Unity to build a dialogue platform based on network analysis and supplied theological briefings to the League of Nations’ Disarmament Commission. In “La Paix par l’Église” (1929) he presented a theoretical framework for the church as a value-rational actor intervening in the international system, applying Max Weber’s typology of social action. This framework later influenced the WCC’s Faith and Order Commission statutes and the introduction of observers to Vatican II.