This review essay examines three intellectual histories focused on fundamental transformations of international law in the early twentieth century. Juan Pablo Scarfi's Hidden History of International Law in the Americas is most interested in debates about a Pan-American international law, meaning the idea that international law might work differently in different regions, which was debated but eventually gave way to the change that Arnulf Becker Lorca, a Lecturer in Public International Law at Georgetown Law, discusses. Becker Lorca's Mestizo International Law is most interested in how the conception that international law applied only to civilized nations transformed into the modern conception that presumes sovereign equality. The Internationalists, by Oona Hathaway and Scott Shapiro, respectively the Gerard C. and Bernice Latrobe Smith Professor of International Law and the Charles F. Southmayd Professor of Law and Professor of Philosophy at Yale Law School, and seeks to understand how the normal (and legal) recourse to force in international relations was replaced by an international law that bans the use of force, except in self-defense. Ideas regarding these issues started to evolve in the late 1800s, but the transformative debates occurred at roughly the same time because the Hague Peace Conferences and the League of Nations allowed contestations over old versus updated understandings of international law to flourish.