5. From the very dawn of civilization, developing human communities sought to establish agreements and pacts which would avoid the arbitrary use of force and enable them to seek a peaceful solution of any controversies which might arise. Alongside the legal systems of the individual peoples there progressively grew up another set of norms which came to be known as ius gentium (the law of the nations). With the passage of time, this body of law gradually expanded and was refined in the light of the historical experiences of the different peoples.

This process was greatly accelerated with the birth of modern States. From the sixteenth century on, jurists, philosophers and theologians were engaged in developing the various headings of international law and in grounding it in the fundamental postulates of the natural law. This process led with increasing force to the formulation of universal principles which are prior to and superior to the internal law of States, and which take into account the unity and the common vocation of the human family.

[Pope John Paul II, Message for the XXXVII World Day of Peace]