Definition
International law is the body of rules, principles, and norms that govern relations among sovereign states and, increasingly, between states and other actors such as international organizations, corporations, and individuals. It establishes the framework within which nations conduct diplomacy, trade, warfare, and dispute resolution.
Two principal divisions define the field:
1. Public international law. The rules governing the rights and obligations of sovereign states in relation to one another and to the international community as a whole. Sources include treaties, customary international law (state practice accepted as legally binding), general principles of law recognized by civilized nations, and subsidiary sources such as judicial decisions and scholarly writing. The United Nations Charter, the Geneva Conventions, and the Vienna Convention on the Law of Treaties are central instruments.
2. Private international law. The rules applied by domestic courts to resolve disputes involving foreign elements — determining which jurisdiction's law governs, which forum has authority, and whether foreign judgments will be recognized. In U.S. usage, this field is more commonly called conflict of laws.
The distinction between public and private international law is foundational. Most historical dictionary definitions, and most popular usage, describe only the public dimension. Researchers who encounter the term without qualification should determine from context which branch is intended.
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Common Language
Modern common usage (Wiktionary): "Set of rules generally regarded and accepted as binding in relations between states and between nations, serving as a framework for the practice of stable and organized international relations."
Historical common usage (Webster's 1913): International law was understood as the law of nations — the body of rules that Christian or civilized states acknowledged as obligatory among themselves, grounded in custom, treaty, and natural reason.
The gap between common and legal meaning is not one of definition so much as one of depth and enforceability. Ordinary usage treats international law as a coherent, binding system analogous to domestic law. Legally, its binding force is contested: there is no sovereign legislature, no compulsory court, and no centralized enforcement mechanism. A researcher using the term in a legal context must attend to whether a given rule is treaty-based (binding on parties), customary (universally binding but difficult to prove), or merely aspirational (soft law). The common understanding obscures these distinctions entirely.
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Common Confusion
International law is frequently conflated with two neighboring concepts that require separate treatment:
Law of nations vs. international law. Historically these terms were used interchangeably, and the historical dictionaries in this corpus treat them as synonyms. In modern usage, law of nations is the older term — derived from the Latin jus gentium and appearing in Blackstone, Vattel, and the U.S. Constitution — while international law is the post-Bentham formulation that became standard after the nineteenth century. The terms overlap substantially, but law of nations in constitutional and early American legal contexts carries specific meaning tied to natural law foundations and piracy jurisdiction that international law, as a modern term, does not automatically import.
Public vs. private international law. As noted in the definition, these are distinct fields. Private international law (conflict of laws) is domestic law applied to cross-border disputes. Public international law governs state-to-state relations. Conflating them produces serious analytical errors in both research and practice.
Jus gentium vs. jus inter gentes. Bouvier's correctly flags this distinction. Jus gentium was the Roman law applicable to transactions between Romans and foreigners — a domestic concept. Jus inter gentes, the law between nations, is the proper ancestor of modern public international law. Historical sources sometimes use jus gentium loosely to mean international law; this requires careful reading.
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Recognized Forms
/SUBTYPES
Customary international law. Rules derived from consistent and general state practice followed out of a sense of legal obligation (opinio juris). Binding on all states that have not persistently objected.
Treaty law. Binding obligations voluntarily assumed by states through written agreements. Governed by the Vienna Convention on the Law of Treaties (1969).
Jus cogens. Peremptory norms from which no derogation is permitted — prohibitions on genocide, slavery, and torture are the standard examples. No treaty can override a jus cogens norm.
Soft law. Non-binding instruments such as UN General Assembly resolutions, declarations, and guidelines that influence state behavior and may eventually crystallize into customary law.
Private international law (conflict of laws). The domestic branch addressing choice of law, jurisdiction, and recognition of foreign judgments in transnational disputes.
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Why It Matters in Research
Terminological instability across time. Prior to Jeremy Bentham's coinage of international law in the late eighteenth century, the standard term was law of nations. Researchers working in pre-nineteenth-century sources — including colonial-era American materials, early Supreme Court opinions, and the founding-era constitutional record — will find law of nations where they expect to find international law. These terms are largely synonymous in that era, but the natural law framework underlying law of nations is not always present in modern international law analysis. Do not assume equivalence without examining context.
The "civilized nations" problem in historical sources. Every historical dictionary entry in this corpus — Black's, Burrill's, Bouvier's — defines international law as applying among "civilized nations" or "Christian states." This is not a minor stylistic artifact. It reflects the nineteenth-century positivist framework that explicitly excluded non-European and non-Christian states from the international legal order. Researchers using these sources to reconstruct historical doctrine must account for this limitation; the framework was actively invoked to deny treaty rights and legal standing to Indigenous nations, colonial subjects, and non-Western states.
Enforcement and the positivist critique. Historical dictionaries present international law as a functioning legal system. The positivist challenge — whether rules without a sovereign enforcer constitute law at all — runs throughout the nineteenth and twentieth century literature and shapes how courts treat international law claims. Austin's denial that international law was law properly so called is a recurring counterpoint in this corpus.
Corpus connections across Law Mind. International law intersects the corpus at multiple levels: trade and tariff law (WTO framework), employment law (jurisdiction over foreign workers and multinational employers), and family law (recognition of foreign divorces and custody orders). Researchers should not treat international law as a self-contained subject; its doctrines flow into nearly every transactional and litigation context involving a foreign element.
Domestic incorporation. The relationship between international law and U.S. domestic law — whether customary international law is automatically federal law, when treaties are self-executing, and how Congress may override treaty obligations — is a distinct and contested body of doctrine. Historical sources do not adequately address this dimension; researchers need modern secondary sources alongside the historical dictionaries.
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Historical Dictionary Support
The historical dictionaries in this corpus present a broadly unified but incomplete picture.
Points of agreement. Black's (both editions) and Burrill's converge on the definition drawn from Kent's Commentaries: international law regulates the intercourse of nations and determines the rights of independent states in peace and war. All sources trace the term to jus inter gentes and treat treaty, custom, and precedent as its foundational sources. This consensus reflects the dominant Anglo-American positivist synthesis of the nineteenth century.
Bouvier's divergence. Bouvier's offers the most theoretically developed entry in the corpus. It distinguishes international law from jus gentium, attributes to states three categories of rights (those arising from statehood itself, those shared with individuals and artificial persons, and those arising from wrongs suffered), and quotes President Woolsey's definition emphasizing international law as the product of free choice among nations rather than natural necessity. Bouvier's also notes the progressive character of the science — its susceptibility to improvement as civilization advances — a framing absent from Black's and Burrill's.
What historical sources miss. None of the historical entries in this corpus addresses the enforcement problem, the positivist critique, the domestic incorporation question, or the exclusion of non-Western states as anything other than background assumption. The modern architecture of international law — UN Charter system, international criminal tribunals, human rights law, WTO dispute resolution — postdates all of these sources entirely. Researchers should treat these entries as reliable guides to nineteenth-century doctrine and intellectual context, not as descriptions of international law as currently applied.
Burrill's entry appears to contain a transcription error in this corpus: a section on interpleader claimants appears mid-definition, interrupting the international law text. Researchers should note this artifact and consult the primary source.
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Jurisdictional Note
The status of international law in U.S. courts depends on its source. Self-executing treaties are supreme federal law under the Supremacy Clause and displace inconsistent state law. Non-self-executing treaties require implementing legislation. Customary international law is generally treated as federal common law, but Congress may override it by statute. State courts apply private international law (conflict of laws) under their own choice-of-law frameworks, which vary significantly across jurisdictions.
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Encyclopedia Cross-Reference
International Trade Law (WTO, Tariffs, and Trade Agreements) — Law Mind Business Organizations & Corporate Law Encyclopedia
International Employment Law Considerations for U.S. Employers — Law Mind Employment & Labor Law Encyclopedia
Recognition of Foreign Divorce Decrees — Law Mind Family Law Encyclopedia
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