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How did Hugo Grotius defend freedom of the seas?

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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 defended the freedom of the seas by arguing that the ocean could not be subjected to national sovereignty and must remain open to all nations for trade and navigation.12

His argument was primarily developed in his 1609 work, Mare Liberum ("The Freedom of the Seas"), which was a chapter extracted from his larger manuscript, De Jure Praedae. Grotius was commissioned by the Dutch East India Company to provide a legal justification for the seizure of a Portuguese vessel. He contended that Spain and Portugal’s claims to a monopoly on trade with the East Indies were illegitimate because they deprived other nations of their natural trading rights.1

By asserting that the high seas are free, Grotius challenged the prevailing practice of maritime states claiming sovereignty over vast ocean territories. His work laid a foundational principle for modern international law, emphasizing that the seas should be accessible to all for peaceful commerce.213