74 So, Venerable Brethren, it is indispensable for the existence of harmonious and lasting contacts and of fruitful relations, that the peoples recognize and observe these principles of international natural law which regulate their normal development and activity. Such principles demand respect for corresponding rights to independence, to life and to the possibility of continuous development in the paths of civilization; they demand, further, fidelity to compacts agreed upon and sanctioned in conformity with the principles of the law of nations.
Source: Summi Pontificatus (Vatican.va)