Chapter 3 traces the historical development of the jus ad bellum from the Peace of Versailles to the adoption of the UN Charter.

This chapter shows how the architects of International Relations (IR) assumed non-academic roles and tried to influence international politics during the 1920s and early 1930s. By focusing on their lives and political interests, it argues that IR came of age not in isolated research laboratories but in the diplomatic milieu of European capitals. The chapter begins with Alfred Zimmern’s Geneva summer schools, a popular annual event for students and practitioners of international politics which became a fixture in the Geneva calendar. The second section surveys a range of public events that IR scholars organised to advance their ideas and to build a disciplinary community. The third section shows how James Shotwell tried to engineer international treaties, specifically the 1924 Geneva Protocol and the 1928 Kellogg–Briand Pact. The fourth section introduces the International Studies Conference (ISC) which provided a permanent platform for exchange between academics and practitioners at annual meetings from 1928 to 1939. The final section illustrates how the 1931 and 1932 ISC sessions on economic policy and free trade sparked public controversy.