"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," he said. "The service 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."
Waging war is not a way of imposing the will of the United States on the world, he said, but a way of seeking a better future for its people.
"The instruments of war do have a role to play in preserving the peace," he said.
Preserving the peace in Oslo Thursday came with a price -- $60 million worth of security preparations. Norwegian police said they had more than 2,000 officers on the streets, along with snipers, canine patrols, and helicopters in the air, in the biggest security operation they have ever mounted for a single person.
Force can be justified on humanitarian grounds, Obama said, because inaction can tear at the world's conscience and lead to more costly intervention later.
But peace can be justified too, he said, and he outlined three ways to build a just and lasting peace in the world.
First, Obama suggested the world find a better way to deal with nations like Iran and North Korea that break or ignore rules and laws.
"If we want a lasting peace, then the words of the international community must mean something," he said. "Those regimes that break the rules must be held accountable. Sanctions must exact a real price."
December 10, 2009
President Obama accepting the Nobel Peace Prize