Pope John XXIII
Pacem in Terris §112
Pacem in Terris: On Establishing Universal Peace in Truth, Justice, Charity, and Liberty
112 Hence justice, right reason, and the recognition of man's dignity cry out insistently for a cessation to the arms race. The stock-piles of armaments which have been built up in various countries must be reduced all round and simultaneously by the parties concerned. Nuclear weapons must be banned. A general agreement must be reached on a suitable disarmament program, with an effective system of mutual control. In the words of Pope Pius XII: "The calamity of a world war, with the economic and social ruin and the moral excesses and dissolution that accompany it, must not on any account be permitted to engulf the human race for a third time." (59)
Source: Pacem in Terris (Vatican.va)