This article is based on an inaugural lecture for the Stevenson Chair in International History, given at the London School of Economics (LSE) in October 2012. It re-examines the origins in Britain in the 1920s of the academic discipline of international history, focusing on the partnership between the LSE and Chatham House. It highlights the differences among the discipline's founders between broader and more tightly defined conceptions of its subject matter and scope, identified respectively with Arnold J. Toynbee on the one hand and with Harold Temperley and Charles Webster on the other. It also underlines the founders' agreement about international history's practical applicability, particularly for analysing and even for helping to prevent the outbreak of major wars. It explores the theme of ‘learning from the past’ by investigating the interconnection between the diplomatic crises of July–August 1914 and October 1962, reappraising John F. Kennedy's use of history to inform statesmanship. The article points to a recurrent pattern in the international conjunctures of 1914, 1939 and 1962 that may be replicating itself again today. It concludes that a knowledge and understanding of international history can indeed yield insights of practical value, though must be drawn on flexibly and with imagination.