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How did Hugo Grotius help establish principles of international law?

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The Code of Hammurabi diorite stela, with carved figures at the top showing Hammurabi seated with cuneiform inscriptions below. — Political philosophy Diorite stela inscribed with the Code of Hammurabi, 18th century bce.

Hugo Grotius, often called the "father of international law," established foundational principles by seeking to minimize bloodshed through a general theory of law.12

His masterpiece, De Jure Belli ac Pacis (1625), argued that a "common law among nations" exists to regulate war between independent powers. Grotius placed natural law at the center of his jurisprudence, asserting its validity regardless of religious belief, while also incorporating religious and utilitarian norms to create a multilayered framework for restraining violence. He maintained that only wars with just causes—such as defense or the restitution of property—should be permitted.3

Additionally, Grotius significantly influenced maritime governance by proposing the doctrine of freedom of the seas in 1609. He argued that the high seas should be open to all nations and not subject to national sovereignty, a principle that eventually became a cornerstone of modern maritime law.4