“Preparedness to use the weapons of war creates the tempers, the quarrels and the crises which lead to the outbreak of war.”

England and the Need for Nations (2006)

"A Community of the Free" address at the The Foreign Policy Association NY, NY (23 June 1976); this is often paraphrased: We cannot be both the world’s leading champion of peace and the world’s leading supplier of the weapons of war.
Pre-Presidency
Context: Sometimes we try to justify this unsavory business on the cynical ground that by rationing out the means of violence we can somehow control the world’s violence. The fact is that we cannot have it both ways. Can we be both the world’s leading champion of peace and the world’s leading supplier of the weapons of war?

Now is the Time to Prevent a Third World War (1950)
Context: The imminence of the threat hovering over civilization requires Christians to disentangle themselves from the war system as completely and as rapidly as they can.... Every Christian has the power to support or to oppose preparedness to wage atomic war.... He can support or oppose the delegating of wider jurisdiction and greater authority to the United Nations Organization through limitations upon national sovereignty. He can support or oppose the policy of settling every conceivable controversy with another nation by pacific means only. He can support or oppose the effort to create the international mind and heart in place of extreme nationalism and narrow patriotism.... He can choose between the way of war and the way of Jesus.

1963, UN speech
Context: The United Nations cannot survive as a static organization. Its obligations are increasing as well as its size. Its Charter must be changed as well as its customs. The authors of that Charter did not intend that it be frozen in perpetuity. The science of weapons and war has made us all, far more than 18 years ago in San Francisco, one world and one human race, with one common destiny. In such a world, absolute sovereignty no longer assures us of absolute security. The conventions of peace must pull abreast and then ahead of the inventions of war. The United Nations, building on its successes and learning from its failures, must be developed into a genuine world security system.

Cavalry Journal (September 1933)

Individualism and Socialism (1933)

1960s, Beyond Vietnam: A Time to Break Silence (1967)
Context: War is not the answer. Communism will never be defeated by the use of atomic bombs or nuclear weapons. Let us not join those who shout war and, through their misguided passions, urge the United States to relinquish its participation in the United Nations. These are days which demand wise restraint and calm reasonableness. We must not engage in a negative anticommunism, but rather in a positive thrust for democracy, realizing that our greatest defense against communism is to take offensive action in behalf of justice. We must with positive action seek to remove those conditions of poverty, insecurity, and injustice, which are the fertile soil in which the seed of communism grows and develops.

1910s, Address to the Knights of Columbus (1915)
Context: Therefore, we should devote ourselves as a preparative to preparedness, alike in peace and war, to secure the three elemental things: one, a common language, the English language; two, the increase in our social loyalty citizenship absolutely undivided, a citizenship which acknowledges no flag except the flag of the United States and which emphatically repudiates all duality of intention or national loyalty; and third, an intelligent and resolute effort for the removal of industrial and social unrest, an effort which shall aim equally at securing every man his rights and to make every man understand that unless he in good faith performs his duties he is not entitled to any rights at all.

Prime Minister's Questions (15 June 1982) http://www.margaretthatcher.org/document/104968
First term as Prime Minister