Jus gentium

The ius gentium or jus gentium (Latin for "law of nations") is a concept of international law within the ancient Roman legal system and Western law traditions based on or influenced by it. The ius gentium is not a body of statute law nor a legal code, but rather customary law thought to be held in common by all gentes ("peoples" or "nations") in "reasoned compliance with standards of international conduct".

Following the Christianization of the Roman Empire, canon law also contributed to the European ius gentium. By the 16th century, the shared concept of the ius gentium disintegrated as individual European nations developed distinct bodies of law, the authority of the Pope declined, and colonialism created subject nations outside the West.