Excerpts from President Obama's speech Thursday accepting the Nobel Peace Prize in Oslo, Norway.

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 lifework, I am living testimony to the moral force of nonviolence. I know there's nothing weak - nothing passive - nothing naive - 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 nonviolent 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.

I raise this point, I begin with this point because in many countries there is a deep ambivalence about military action today, no matter what the cause. And at times, this is joined by a reflexive suspicion of America, the world's sole military superpower.

But the world must remember that it was not simply international institutions - not just treaties and declarations - that brought stability to a post-World War II world. Whatever mistakes we have made, the plain fact is this: The United States of America has helped underwrite global security for more than six decades with the blood of our citizens and the strength of our arms. The service and sacrifice of our men and women in uniform has promoted peace and prosperity from Germany to Korea, and enabled democracy to take hold in places like the Balkans. We have borne this burden not because we seek to impose our will. We have done so out of enlightened self-interest - because we seek a better future for our children and grandchildren, and we believe that their lives will be better if others' children and grandchildren can live in freedom and prosperity.

So, yes, the instruments of war do have a role to play in preserving the peace. And yet this truth must coexist with another - that no matter how justified, war promises human tragedy. The soldier's courage and sacrifice is full of glory, expressing devotion to country, to cause, to comrades in arms. But war itself is never glorious, and we must never trumpet it as such.

So part of our challenge is reconciling these two seemingly irreconcilable truths - that war is sometimes necessary, and war at some level is an expression of human folly. Concretely, we must direct our effort to the task that President Kennedy called for long ago. "Let us focus," he said, "on a more practical, more attainable peace, based not on a sudden revolution in human nature but on a gradual evolution in human institutions." A gradual evolution of human institutions. . . .

Agreements among nations. Strong institutions. Support for human rights. Investments in development. All these are vital ingredients in bringing about the evolution that President Kennedy spoke about. And yet, I do not believe that we will have the will, the determination, the staying power, to complete this work without something more - and that's the continued expansion of our moral imagination; an insistence that there's something irreducible that we all share.

As the world grows smaller, you might think it would be easier for human beings to recognize how similar we are; to understand that we're all basically seeking the same things; that we all hope for the chance to live out our lives with some measure of happiness and fulfillment for ourselves and our families. . . .

We do not have to think that human nature is perfect for us to still believe that the human condition can be perfected. We do not have to live in an idealized world to still reach for those ideals that will make it a better place. The nonviolence practiced by men like Gandhi and King may not have been practical or possible in every circumstance, but the love that they preached - their fundamental faith in human progress - that must always be the North Star that guides us on our journey.

For if we lose that faith - if we dismiss it as silly or naive; if we divorce it from the decisions that we make on issues of war and peace - then we lose what's best about humanity. We lose our sense of possibility. We lose our moral compass.

Like generations have before us, we must reject that future. As Dr. King said at this occasion so many years ago, "I refuse to accept despair as the final response to the ambiguities of history. I refuse to accept the idea that the 'isness' of man's present condition makes him morally incapable of reaching up for the eternal 'oughtness' that forever confronts him."

Let us reach for the world that ought to be - that spark of the divine that still stirs within each of our souls.

Somewhere today, in the here and now, in the world as it is, a soldier sees he's outgunned, but stands firm to keep the peace. Somewhere today, in this world, a young protester awaits the brutality of her government, but has the courage to march on. Somewhere today, a mother facing punishing poverty still takes the time to teach her child, scrapes together what few coins she has to send that child to school - because she believes that a cruel world still has a place for that child's dreams.

Let us live by their example. We can acknowledge that oppression will always be with us, and still strive for justice. We can admit the intractability of deprivation, and still strive for dignity. Clear-eyed, we can understand that there will be war, and still strive for peace. We can do that - for that is the story of human progress; that's the hope of all the world; and at this moment of challenge, that must be our work here on Earth.