International law and domestic law differ in four ways that matter: where their authority comes from, who they bind, how their rules are created, and how those rules get enforced. Domestic law flows down from a single sovereign and reaches everyone inside a country’s borders whether they consented or not. International law runs horizontally between sovereign states that are treated as legal equals, so it generally binds a country only to the extent that country has agreed to be bound. That single structural gap explains almost every practical difference between the two systems, including the one people notice first: international law has no police force behind it.
Where the Authority Comes From
Domestic law rests on a vertical chain of command. In the United States, the Constitution sits at the top and creates three branches that check one another: Congress passes laws, the President signs them, and courts can strike them down as unconstitutional.1United States Courts. Court Role and Structure You don’t have to agree with a law for it to apply to you. Stand inside the country’s jurisdiction and its rules reach you.
International law works on a horizontal plane. Because sovereign states are considered legal equals, no state has inherent authority over another, and the system runs on consent. States are generally bound only by the obligations they have accepted, either by signing a treaty or through longstanding practice they treat as legally required.2Legal Information Institute. International Law The Vienna Convention on the Law of Treaties expresses the core commitment with the principle of pacta sunt servanda: every treaty in force must be performed by its parties in good faith.3United Nations. Vienna Convention on the Law of Treaties Obligation is mutual, not commanded from above.
Who Each System Governs
Domestic law governs everyone and everything inside a country’s territory. Individuals, businesses, nonprofits, and the government itself. Citizenship isn’t the trigger; presence is.
International law was built by states to govern their dealings with each other, and states are still its primary subjects. Treaties cover diplomacy, trade, maritime boundaries, armed conflict, and many other areas where nations need shared rules. International organizations like the United Nations are also governed by international law, operating under charters that define their powers.4United Nations. International Law and Justice
The reach has widened over the past century. International human rights law creates protections that run to individuals, not just to states. International criminal law holds individual people accountable for the gravest offenses, and the International Criminal Court has jurisdiction over individuals charged with genocide, crimes against humanity, war crimes, and the crime of aggression.5International Criminal Court. Rome Statute of the International Criminal Court Multinational corporations sit awkwardly in between. Frameworks such as the OECD Guidelines for Multinational Enterprises set standards for cross-border corporate conduct, but those remain voluntary recommendations rather than binding law.
How the Rules Get Made
Domestic legal systems have identifiable institutions that make law. A legislature drafts and votes on statutes. Courts create binding rules through precedent, where a decision in one case governs similar cases that follow.6Constitution Annotated. Judicial Precedent and Constitutional Interpretation Executive agencies issue regulations. The particulars vary by country, but the common thread is that named institutions have the authority to bind everyone.
International law has no legislature. Its rules come from decentralized sources listed in Article 38 of the Statute of the International Court of Justice: treaties between states, customary international law that develops when states consistently follow a practice out of a sense of legal obligation, general principles recognized across the world’s major legal systems, and judicial decisions and scholarly writings as subsidiary tools of interpretation.7International Court of Justice. Statute of the International Court of Justice A treaty binds only the states that become parties to it.3United Nations. Vienna Convention on the Law of Treaties Custom requires both the practice and the belief that the practice is legally required, known as opinio juris, which is what separates a legal custom from a mere habit.8United Nations International Law Commission. Draft Conclusions on Identification of Customary International Law
There is a narrow category where consent doesn’t save you. Peremptory norms, or jus cogens, are rules considered so fundamental that no treaty can override them. The International Law Commission has identified examples including the prohibitions on genocide, torture, slavery, aggression, racial discrimination and apartheid, along with the basic rules of international humanitarian law and the right of self-determination.9United Nations International Law Commission. Peremptory Norms of General International Law (Jus Cogens) A treaty that violates one of these norms is void.
How the Rules Get Enforced
This is where the two systems separate most sharply. Domestic law comes with a full enforcement apparatus. Police investigate and arrest. Courts have compulsory jurisdiction and can summon you whether you want to appear or not. When you lose, the state can collect: fines, imprisonment, seizures, injunctions backed by contempt. Your cooperation isn’t required.
International law has no equivalent machinery. There is no world police, no global prosecutor with general authority, and no court that can force a country to appear against its will. Compliance runs on voluntary participation, political pressure, reputation costs, and the practical benefits states gain from keeping their commitments. When one state breaches, the injured state’s main tools are countermeasures: proportional, reversible acts of non-compliance meant to pressure the violator back into line. Economic sanctions, whether imposed by individual countries or authorized by the UN Security Council, are the most visible form. The Security Council can authorize broader collective action, including the use of force, but any of its five permanent members can veto a resolution, which regularly paralyzes the body on politically sensitive matters.10United Nations. Charter of the United Nations – Article 94
International courts exist, but their reach is narrower than a domestic court’s. The International Court of Justice, the principal judicial body of the United Nations, can hear a dispute between states only if both sides have consented to its jurisdiction, whether through a special agreement, a clause in a treaty, or a standing declaration.11International Court of Justice. How the Court Works A state that hasn’t consented cannot be brought before the ICJ. Even after a ruling, Article 94 of the UN Charter provides that if a party fails to comply, the other party can turn to the Security Council, which “may, if it deems necessary, make recommendations or decide upon measures to be taken to give effect to the judgment.”10United Nations. Charter of the United Nations – Article 94 That “may” does a lot of work, and the veto again shapes what actually happens.
The ICC targets individuals rather than states, but it is designed as a court of last resort. Under its complementarity principle, a case is inadmissible if a national court with jurisdiction is genuinely investigating or prosecuting it, so the ICC steps in only when domestic courts are unwilling or unable to act. Even then, the court depends on states to arrest suspects and carry out sentences, and several major powers, including the United States, are not parties to the Rome Statute.5International Criminal Court. Rome Statute of the International Criminal Court
How International Law Reaches Into a Domestic System
The two systems aren’t sealed off from each other. The practical question, for most people, is whether an international obligation is actually enforceable inside a country’s courts. Countries answer differently, and the answer changes what rights you can assert.
Treaties in U.S. Law
Under the Supremacy Clause, treaties made under the authority of the United States are “the supreme Law of the Land,” together with the Constitution and federal statutes.12Constitution Annotated. Article VI – Supreme Law, Clause 2 In practice, though, not every treaty operates that way. The Supreme Court distinguishes self-executing treaties, which take effect as domestic law upon ratification, from non-self-executing treaties, which create an international commitment but cannot be enforced in American courts until Congress passes implementing legislation.13Justia US Supreme Court. Medellin v. Texas, 552 U.S. 491 (2008) That distinction often decides whether a treaty gives an individual enforceable rights or is just a promise between governments.
Suing a Foreign Government
Foreign states generally cannot be sued in American courts without their consent, under the doctrine of sovereign immunity.14Constitution Annotated. Suits Involving Foreign States Congress codified the rules in the Foreign Sovereign Immunities Act, which starts from a presumption of immunity but carves out exceptions. The most important is the commercial activity exception: a foreign state loses immunity when the suit is based on commercial activity the state carried on in the United States, on an act performed in the United States in connection with its commercial activity elsewhere, or on an act abroad in connection with its commercial activity that causes a direct effect in the United States.15Office of the Law Revision Counsel. 28 U.S. Code 1605 – General Exceptions to the Jurisdictional Immunity of a Foreign State When a government enters the marketplace, it plays by marketplace rules.
Enforcing Foreign Awards and Judgments
Cross-border private disputes are often routed through international arbitration by contract. The 1958 New York Convention creates a framework for enforcing arbitration awards across national borders and has been adopted by over 170 countries. The grounds for refusing enforcement are narrow and mostly procedural, such as an invalid agreement, lack of proper notice, or arbitrators exceeding the scope of the dispute.16New York Convention. United Nations Convention on the Recognition and Enforcement of Foreign Arbitral Awards Enforcing a foreign court judgment is harder. No federal law governs recognition of foreign-country court judgments in the United States. Most states have adopted a version of the Uniform Foreign-Country Money Judgments Recognition Act, which generally requires the judgment to be final, conclusive, and enforceable where it was issued, and which excludes judgments imposing taxes, fines, or penalties.
Why the Difference Matters in Practice
The structural gap between the two systems is not just theoretical. It decides whether you can enforce a right, collect on a judgment, or hold a foreign government accountable. Domestic law hands you a courthouse, a sheriff, and a process that works whether the other side cooperates or not. International law hands you a framework that works well when states play along and struggles when a powerful one decides not to. Knowing which system governs your situation is the first step to knowing what remedy is actually on the table.