The horrors of modern war shocked sensibilities enough that by the 1920s there were active efforts to outlaw war entirely. The idea's proponents would face obstacles from disinterested governments and even conflicts among each other. But by decade's end the world had come together in agreement with their principals. 

Bibliography for this episode: 

1. Hathaway, Oona A. and Scott J. Shapiro The Internationalists: How a Radical Plan to Outlaw War Remade the World Simon and Schuster 2017

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