How is international law enforced?

International law differs from domestic law. In the United States, the federal and state governments enforce domestic American law. However, in terms of international law, no government or international organization enforces international law. Although the United Nations Security Council may pass measures authorizing enforcement, the enforcement entity envisioned (Art. 43) to carry out such measures never materialized due to the failure of member states to provide the necessary resources (such as troops). (An enforcement body should not be confused with existing United Nations peacekeeping forces, whose function is to maintain peace and security, not to enforce breaches of international law.)

How are international disputes resolved?

International disputes sometimes result in armed conflict between states, despite the prohibition of aggressive force (meaning, force not used in self-defense) (United Nations Charter, Art. 2(4)). However, most disputes between states are settled peacefully. Pacific settlement is often reached by diplomatic means, whereby states voluntarily comply with international law amidst pressure from other states. Another peaceful settlement mechanism is submission of the matter by the disputing states to an international tribunal, court, or arbitration.

What are the sources of international law?

• International agreements
• Customary law
• jus cogens (meaning "strong law" or "compelling law")
• resolutions passed by international organizations (in some circumstances)
• to an extent, decisions of international tribunals, courts, and arbitrations (depending upon the underlying agreement to arbitrate)
• some general principles of law
• judicial decisions and academic treatises (but only as auxiliary sources)

International agreements (such as treaties, conventions, covenants and protocols) between states are the oldest sources of international law. The earliest known treaty dates back to 1380 B.C., to an alliance between the Hittite King Suppiluliuma I and Aziras of Amurru (a North Syrian province of the Egyptian empire).

Customary law is law developed out of a practice by states of adhering to a particular custom out of a sense of obligation.

Jus cogens describes peremptory norms of international law from which no derogation by treaty is permitted. (Vienna Convention on the Law of Treaties, Arts. 53, 64). For example, nations may not contract out of the law forbidding slavery.

In special circumstances, international organizations can create binding law. Resolutions passed by the United Nations Security Council under Chapter VII of the United Nations Charter may be binding on member states (Arts. 41, 42, 48, 49). An example of such a resolution is one that orders sanctions against a state in response to a breach of international law which threatens international peace and security.

Opinions issued by international tribunals (including courts and arbitration) comprise law to the extent that they are binding upon the states-parties to the proceeding. Such decisions are not binding on non-parties, but may serve to reveal the composition of international law to other states and tribunals.

Other sources of international law may be inferred from those available to the International Court of Justice (the "ICJ," also known as "the World Court," the main judicial organ of the United Nations). In addition to the sources already mentioned, the World Court may rely on general legal principles "as recognized by civilized nations" in deducing international law (Statute of the ICJ, Art. 38). The Court may also draw upon, as secondary sources, "judicial decisions and teachings of the most highly qualified publicists of the various nations" in determining the rules of international law (Statute of the ICJ, Art. 38).