83 In order to build up peace above all the causes of discord among men, especially injustice, which foment wars must be rooted out. Not a few of these causes come from excessive economic inequalities and from putting off the steps needed to remedy them. Other causes of discord, however, have their source in the desire to dominate and in a contempt for persons. And, if we look for deeper causes, we find them in human envy, distrust, pride, and other egotistical passions. Man cannot bear so many ruptures in the harmony of things. Consequently, the world is constantly beset by strife and violence between men, even when no war is being waged. Besides, since these same evils are present in the relations between various nations as well, in order to overcome or forestall them and to keep violence once unleashed within limits it is absolutely necessary for countries to cooperate more advantageously and more closely together and to organize together international bodies and to work tirelessly for the creation of organizations which will foster peace.
Source: Gaudium et Spes (Vatican.va)