This book is the result of three years of hard work. But it builds upon centuries of inspired thinking and practical efforts to constrain war. As the chapters in this volume outline, the efforts to constrain violence and impose accountability on aggressors include Hammurabi's Code, the 1899 and 1907 Hague Treaties with their Martens Clauses, the Kellogg–Briand Pact, the Nuremberg and Tokyo trials and judgments, the establishment of the United Nations, the decisions of international courts, arbitral tribunals and fact-finding commissions, the development of just war doctrines and the Responsibility to Protect, and, most recently, the establishment of the International Criminal Court and the activation of the Kampala Amendments on the crime of aggression. These efforts show that even during the darkest days of war, men and women have never given up the dream of a world at peace in which violence is the exception, rather than the rule, and in which lawful violence is defined and cabined by robust legal frameworks.

This volume would never have been possible but for the generosity – and leadership – of both Ben and Don Ferencz, who helped with its conceptual framing, funding, and implementation both in their individual capacities and through the generosity of the Planethood Foundation. Ben's faith in the rule of law and its capacity to serve the interest of peace has been an inspiration for more than seven decades. Don, equally, has become a passionate advocate for the rule of law in the service of peace. I, personally, and the world entire, are indebted to them for their perseverance, clear-sightedness, wisdom, and faith in humankind's ability to do better than it has done in the past.

I am also grateful to Harris Institute Fellows Fizza Batool, Madaline George, Kristin Smith, and Tamara Slater, who worked on the volume from conception to realization, and to Bethel Mandefro, the Institute's Program Coordinator and Office Manager, who helped with the logistics of our St. Louis Conference in 2015 and with shepherding the volume through publication. It would be remiss to omit the many students who worked on the volume as well, including Kaitlyn Byrne, Kelly Mullen, Jesus A. Osete, Brittany Sanders, and Caroline Tunca. I would also like to thank John Berger, my editor at Cambridge University Press, who has helped me with this as well as other publications.