National law is a body of legal rules that governs the decisions of a nation. The United States has federal laws that are signed by the president and published in the United States Code. Other states have a constitution, which is a statement of basic principles that regulate the conduct of government. Sometimes, a national constitution is also justiciable in a court of law.

Historically, the concept of a nation-state developed rapidly after the 1648 Peace of Westphalia. Many of the earliest peace treaties were concluded between Greek city-states.

Early international law primarily dealt with relations between individual nations. During the mid-19th century, a growing number of treaties created bodies to regulate the behavior of states. In 1864, a convention called the Hague Convention was passed.

In the 20th century, the concept of natural rights became more important. Natural rights remained influential in international politics through the republican revolutions of the United States.

Human rights law is another type of law that is often used by a nation to protect its citizens. It is found in legislation, national constitutions, and unwritten common law.

When a nation ratifies a treaty, it may automatically incorporate the interpretation of that international law into its own law. This process is known as a “general transformation.”

A common method of incorporating a treaty into national law is through a “transformational device.” Specific devices are employed by different states.

For example, in the United States, a treaty’s recitation of war rules is referred to as a “Lieber Code.” Similarly, a treaty’s rules of recognition are construed according to the customs of civilized nations.