Gaudium et Spes concludes a section on war and peace, starting with a nod to national leaders who have worked for peace:
In the meantime, efforts which have already been made and are still underway to eliminate the danger of war are not to be underrated. On the contrary, support should be given to the good will of the very many leaders who work hard to do away with war, which they abominate. These (leaders), although burdened by the extremely weighty preoccupations of their high office, are nonetheless moved by the very grave peacemaking task to which they are bound, even if they cannot ignore the complexity of matters as they stand. We should fervently ask God to give these (leaders) the strength to go forward perseveringly and to follow through courageously on this work of building peace with vigor. It is a work of supreme love for (hu)mankind. Today it certainly demands that they extend their thoughts and their spirit beyond the confines of their own nation, that they put aside national selfishness and ambition to dominate other nations, and that they nourish a profound reverence for the whole of humanity, which is already making its way so laboriously toward greater unity.
The notion of an institute devoted to the study of peace has popped up now and again. I’m not aware of any nation in which it has been put into practce, yet the bishops mention it:
The problems of peace and of disarmament have already been the subject of extensive, strenuous and constant examination. Together with international meetings dealing with these problems, such studies should be regarded as the first steps toward solving these serious questions, and should be promoted with even greater urgency by way of yielding concrete results in the future.
Peace begins with attitudes of the human heart and will, not international efforts, as pacifists will tell you:
Nevertheless, (people) should take heed not to entrust themselves only to the efforts of some, while not caring about their own attitudes. For government officials who must at one and the same time guarantee the good of their own people and promote the universal good are very greatly dependent on public opinion and feeling. It does them no good to work for peace as long as feelings of hostility, contempt and distrust, as well as racial hatred and unbending ideologies, continue to divide men and place them in opposing camps. Consequently there is above all a pressing need for a renewed education of attitudes and for new inspiration in public opinion. Those who are dedicated to the work of education, particularly of the young, or who mold public opinion, should consider it their most weighty task to instruct all in fresh sentiments of peace. Indeed, we all need a change of heart as we regard the entire world and those tasks which we can perform in unison for the betterment of our race.
But we should not let false hope deceive us. For unless enmities and hatred are put away and firm, honest agreements concerning world peace are reached in the future, humanity, which already is in the middle of a grave crisis, even though it is endowed with remarkable knowledge, will perhaps be brought to that dismal hour in which it will experience no peace other than the dreadful peace of death. But, while we say this, the Church of Christ, present in the midst of the anxiety of this age, does not cease to hope most firmly. She intends to propose to our age over and over again, in season and out of season, this apostolic message: “Behold, now is the acceptable time for a change of heart; behold! now is the day of salvation.” (2 Cor. 2:6.)