This lecture, delivered on 4 May 2026 at the George P. Shultz National Foreign Affairs Training Center in Arlington, Virginia as part of the Foreign Service Orientation course, was written and presented by Dr Thomas Grant, Senior Fellow at Policy Exchange.

The NFATC is the U.S government’s premier training facility for foreign affairs professionals, housing the Foreign Service Institute and providing comprehensive education in diplomacy, languages, leadership, and technology.

In his lecture, Dr Grant explains that international law is real law, but that there are significant differences between international law and domestic law. International law binds chiefly through consent, expressed by states through treaties and other methods.

 Sovereignty is international law’s central puzzle. International law claims to command nation-states, yet nation-states are sovereign and, so, by definition, not subject to any other power. The tension this puzzle creates diplomats must understand rather than pretend away.

Dr Grant also argues that:

• We should push back against the idea that “international law” simply means moral righteousness. International law is not a code of virtue, nor a slogan meaning “the decent thing to do”; it has to be found in formal legal sources, which is to say treaties, custom, or general principles recognised by civilized nations.
• Not every declaration or wish is international law. Treaties bind only their parties; political communiqués, UN expert opinions, NGO statements, and foreign domestic laws can matter politically, but they do not automatically bind a sovereign nation as law.
• Customary international law is especially prone to misuse. For there to exist a customary rule, there needs to exist both state practice and a belief that the practice is legally required. Without both, repeated diplomatic habits or advocacy claims are not law.
• International law has consequences for geopolitical questions of great moment—nuclear weapons, land mines, cluster munitions, the law of the sea, piracy on the high seas, territorial and maritime boundaries, to name a few. Policy makers and the general public, if they care about war and peace, arms control, trade, investment, the treatment of citizens abroad, navigation, diplomacy, or courts need to pay attention to international law.
• The UN is important but not a world government. States have not conferred power on the UN as a global legislature, and the International Court of Justice does not bind states unless they have consented to its jurisdiction.
• International law is a tool of statecraft. This matters because diplomats and other officials constantly hear legal claims in negotiations, disputes, and public argument. They need to know which claims are law, which are politics, and which are merely advocacy in the guise of law.

In a Foreword to the lecture, the Hon Michael R. Pompeo, seventieth Secretary of State of the United States (2018 – 2021) warns that “international law is too often abused by activists who seek to use it as a cudgel against Western governments, and wielded as a weapon by adversaries who flout every law on the books while using our own legal norms against us.”