When Did the Science of International Law Emerge?

There is no universally accepted answer to this question. However, in my opinion, the year 1625 can be considered the birth year of the science of international law. Why this particular year? Because in 1625, the world witnessed the publication of Hugo Grotius’ seminal work, De Jure Belli ac Pacis (On the Law of War and Peace). Grotius wrote this treatise with the aim of promoting justice in international relations. It was the concept of justice that became the central guiding principle—what we might call the “regulative idea”—of the new discipline. For this reason, Grotius is often regarded as the “father of international law.”

This makes the year 2025 especially significant: it marks the 400th anniversary of the first publication of Grotius’ foundational treatise. In many ways, this year is a jubilee for the science of international law, writes the Chairman of the Committee on Foreign Policy and Interparliamentary Cooperation of the Verkhovna Rada, Oleksandr Merezhko, in a Facebook post.

Interestingly, there is a historical paradox here. The science of international law, as represented by Grotius’ work, appeared before the formal system of international law itself, which is generally dated to 1648, with the signing of the Peace of Westphalia. In other words, international legal theory preceded the actual establishment of a European international legal order.

As for the photo, it shows another important work by Hugo Grotius—Mare Liberum (The Free Sea), first published in 1609. This book anticipated some of the key ideas that would later be fully developed in his 1625 treatise and laid the groundwork for the modern concept of international maritime law.