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Rules governing relations among Greek city-states and within the Roman Empire, focused on envoys, treaties, and reciprocity based on self-interest.
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Hugo Grotius publishes De Jure Belli ac Pacis, systematizing international law by combining natural law, treaties, and state practice.
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Peace of Westphalia ends Thirty Years War, establishing sovereign states as the foundation of international society and law.
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Expansion of rules on seas, diplomacy, consular relations, and state responsibility; multilateral conventions regulate fisheries, cables, slavery.
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Jeremy Bentham coins the term "international law," replacing "law of nations."
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Congress of Vienna promotes long-term European peace, leading to multilateral conventions and early international organizations like Rhine and Danube Commissions.
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John Austin defines law as sovereign commands with sanctions, classifying international law as "positive morality" rather than true law.
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International Telegraph Union (now ITU) created as first administrative international organization.
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Universal Postal Union established for postal cooperation.
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League of Nations and Permanent Court of International Justice (PCIJ) founded to prevent war and settle disputes.
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Kellogg-Briand Pact attempts to outlaw war directly.
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New Geneva Conventions recast laws of war.
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UN Charter signed, creating United Nations with 51 members, prohibiting force, and establishing International Court of Justice (ICJ) as successor to PCIJ.
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Horizontal and vertical expansion of international law into human rights, economic affairs, environment, and individual duties via treaties and soft law; UN grows to 192 members.
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UN establishes International Law Commission for progressive development and codification of international law.