“The world has only a limited time to change its custom of resolving conflicts violently.”

2000s, 2003, Invasion of Iraq (March 2003)

Epilogue: Ecological Literacy
The Web of Life (1996)

Anatol Rapoport, Conflict in man-made environment. Harmondsworth: Penguin Books, 1974; As cited in M.J. Apter, ‎J.H. Kerr, ‎S. Murgatroyd (1993) Advances in Reversal Theory. p. 63-64
1970s and later

Source: Rules for Radicals: A Practical Primer for Realistic Radicals (1971), p. 21

Interviewed by the Agence France Presse (AFP), in Cairo (30 January 1953), quoted in an article in Le Monde, entitled "Les Condamnations de Nuremberg seront responsible de l'horreur de la prochaine guerre, affirme Otto Skorzeny."
Context: War is inevitable, and this time, it will be truly world wide. It will unravel everywhere and there will be no limit to its battlefields. The condemnations of Nuremberg will be one of the main reasons, which will cause this war to be a conflict whose horror will be unparalleled. These condemnations gave birth, in fact, to a new conception which makes the victor a hero and the vanquished an odious criminal. By this fact, each leader will wage war like a demon in order not to be the loser and become, consequently, a criminal. All the atrocities that can be imagined by man, will be committed during this next war, in order to prevent the enemy from acquiring victory. What I have just said, I have repeated to the American representatives and I have warned them that all of the mothers of the entire world will one day curse America.

2009, Nobel Prize acceptance speech (December 2009)
Context: In today's wars, many more civilians are killed than soldiers; the seeds of future conflict are sown, economies are wrecked, civil societies torn asunder, refugees amassed, children scarred.
I do not bring with me today a definitive solution to the problems of war. What I do know is that meeting these challenges will require the same vision, hard work, and persistence of those men and women who acted so boldly decades ago. And it will require us to think in new ways about the notions of just war and the imperatives of a just peace.
We must begin by acknowledging the hard truth: We will not eradicate violent conflict in our lifetimes. There will be times when nations — acting individually or in concert — will find the use of force not only necessary but morally justified.
I make this statement mindful of what Martin Luther King Jr. said in this same ceremony years ago: "Violence never brings permanent peace. It solves no social problem: it merely creates new and more complicated ones." As someone who stands here as a direct consequence of Dr. King's life work, I am living testimony to the moral force of non-violence. I know there's nothing weak — nothing passive — nothing naïve — in the creed and lives of Gandhi and King.
But as a head of state sworn to protect and defend my nation, I cannot be guided by their examples alone. I face the world as it is, and cannot stand idle in the face of threats to the American people. For make no mistake: Evil does exist in the world. A non-violent movement could not have halted Hitler's armies. Negotiations cannot convince al Qaeda's leaders to lay down their arms. To say that force may sometimes be necessary is not a call to cynicism — it is a recognition of history; the imperfections of man and the limits of reason.

Concurring, Western Pacific Railroad Corp. v. Western Pacific Railroad Co., 345 U.S. 247, 270 (1953).
Judicial opinions

Original German:Die Logik erfüllt die Welt; die Grenzen der Welt sind auch ihre Grenzen. Wir können also in der Logik nicht sagen: Das und das gibt es in der Welt, jenes nicht.Das würde nämlich scheinbar voraussetzen, dass wir gewisse Möglichkeiten ausschließen, und dies kann nicht der Fall sein, da sonst die Logik über die Grenzen der Welt hinaus müsste; wenn sie nämlich diese Grenzen auch von der anderen Seite betrachten könnte. Was wir nicht denken können, das können wir nicht denken; wir können also auch nicht sagen, was wir nicht denken können.
1920s, Tractatus Logico-Philosophicus (1922)
Context: Logic pervades the world: the limits of the world are also its limits. So we cannot say in logic, "The world has this in it, and this, but not that." For that would appear to presuppose that we were excluding certain possibilities, and this cannot be the case, since it would require that logic should go beyond the limits of the world; for only in that way could it view those limits from the other side as well. We cannot think what we cannot think; so what we cannot think we cannot say either. (5.61)