Today, every inhabitant of this planet must contemplate the day when this planet may no longer be habitable. Every man, woman and child lives under a nuclear sword of Damocles, hanging by the slenderest of threads, capable of being cut at any moment by accident, or miscalculation, or by madness. The weapons of war must be abolished before they abolish us. In an address before the General Assembly of the United Nations on September 25, 1961.

People never lie so much as after a hunt, during a war or before an election.

If there is ever another war in Europe, it will come out of some damned silly thing in the Balkans. Almost perfectly describes World War I, which occured well after his death.

Anyone who has ever looked into the glazed eyes of a soldier dying on the battlefield will think hard before starting a war.

The United States, as the world knows, will never start a war. We do not want a war. We do not now expect a war. This generation of Americans has already had enough — more than enough — of war and hate and oppression. We shall be prepared if others wish it. We shall be alert to try to stop it. But we shall also do our part to build a world of peace where the weak are safe and the strong are just. We are not helpless before that task or hopeless of its success. Address at The American University, Washington D.C. (10 June 1963)

We will not prematurely or unnecessarily risk the costs of a worldwide nuclear war in which even the fruits of victory would be ashes in our mouth — but neither shall we shrink from that risk any time it must be faced. Radio address about the Cuban missile crisis (22 October 1962)

A wall [is] a hell of a lot better than war. Upon hearing about the construction of the Berlin Wall.

Mankind must put an end to war or war will put an end to mankind.

Be polite; write diplomatically; even in a declaration of war one observes the rules of politeness.

We must carry the war into every corner the enemy happens to carry it: to his home, to his centers of entertainment; a total war. It is necessary to prevent him from having a moment of peace, a quiet moment outside his barracks or even inside; we must attack him wherever he may be, make him feel like a cornered beast wherever he may move.

The difference of race is one of the reasons why I fear war may always exist; because race implies difference, difference implies superiority, and superiority leads to predominance. Speech in the House of Commons (1849-02-01)

That doctrine [of peace at any price] has done more mischief than any I can well recall that have been afloat in this country. It has occasioned more wars than any of the most ruthless conquerors. It has disturbed and nearly destroyed that political equilibrium so necessary to the liberties and the welfare of the world. Speech to the House of Lords (1844-04-24)