When you want to fool the world, tell the truth.

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.

What kind of peace do we seek? Not a Pax Americana enforced on the world by American weapons of war. Not the peace of the grave or the security of the slave. I am talking about genuine peace, the kind of peace that makes life on earth worth living, the kind that enables men and nations to grow and to hope and to build a better life for their children — not merely peace for Americans but peace for all men and women — not merely peace in our time but peace for all time. Address at The American University, Washington D.C. (10 June 1963)

In the long history of the world, only a few generations have been granted the role of defending freedom in its hour of maximum danger. I do not shrink from this responsibility — I welcome it. I do not believe that any of us would exchange places with any other people or any other generation. The energy, the faith, the devotion which we bring to this endeavor will light our country and all who serve it — and the glow from that fire can truly light the world.
And so, my fellow Americans: ask not what your country can do for you — ask what you can do for your country.
My fellow citizens of the world: ask not what America will do for you, but what together we can do for the freedom of man. Inaugural Address (20 January 1961)

If a beachhead of cooperation may push back the jungle of suspicion, let both sides join in creating a new endeavor, not a new balance of power, but a new world of law, where the strong are just and the weak secure and the peace preserved.
All this will not be finished in the first one hundred days. Nor will it be finished in the first one thousand days, nor in the life of this Administration, nor even perhaps in our lifetime on this planet. But let us begin. Inaugural Address (20 January 1961)

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)

Assassination has never changed the history of the world. Speech in the House of Commons (1865-05-01)

I speak of peace, therefore, as the necessary rational end of rational men. I realize that the pursuit of peace is not as dramatic as the pursuit of war — and frequently the words of the pursuer fall on deaf ears. But we have no more urgent task. Address at The American University, Washington D.C. (10 June 1963)

The path we have chosen for the present is full of hazards, as all paths are; but it is one of the most consistent with our character and our courage as a nation and our commitments around the world. The cost of freedom is always high — but Americans have always paid it. And one path we shall never choose, and this is the path of surrender or submission. Our goal is not victory of might but the vindication of right — not peace at the expense of freedom, but both peace and freedom, here in this hemisphere and, we hope, around the world. God willing, that goal will be achieved. Thank you, and good night. Cuban Missile Crisis speech (22 October 1962)

The world has changed far more in the past 100 years than in any other century in history. The reason is not political or economic but technological — technologies that flowed directly from advances in basic science.

The world is weary of statesmen whom democracy has degraded into politicians.

At present the peace of the world has been preserved, not by statesmen, but by capitalists Letter to Mrs. Sarah Brydges Willyams (1863-10-17)

I have the same goal I've had ever since I was a girl. I want to rule the world.

As scientists, we understand the dangers of nuclear weapons and their devastating effects, and we are learning how human activities and technologies are affecting climate systems in ways that may forever change life on Earth. As citizens of the world, we have a duty to alert the public to the unnecessary risks that we live with every day, and to the perils we foresee if governments and societies do not take action now to render nuclear weapons obsolete and to prevent further climate change...There’s a realization that we are changing our climate for the worse. That would have catastrophic effects. Although the threat is not as dire as that of nuclear weapons right now, in the long term we are looking at a serious threat. At a press conference for the Bulletin of the Atomic Scientists (2007-01-17)