OSLO — President Barack Obama entered the pantheon of Nobel Peace Prize winners with humble words today, acknowledging his own few accomplishments while delivering a robust defense of war and promising to use the prestigious prize to "reach for the world that ought to be."

A wartime president honored for peace, Obama became the first sitting U.S. president in 90 years and the third ever to win the prize.

Just nine days after ordering 30,000 more U.S. troops into battle in Afghanistan, Obama delivered a Nobel acceptance speech that he saw as a treatise on war's use and prevention. He crafted much of the address himself and the scholarly remarks were nearly twice as long as his inaugural address.

In them, Obama refused to renounce war for his nation or under his leadership, saying defiantly that "I face the world as it is" and that he is obliged to protect and defend the United States.

"A nonviolent movement could not have halted Hitler's armies. Negotiations cannot convince al-Qaida's leaders to lay down their arms," Obama said. "To say that force is sometimes necessary is not a call to cynicism, it is a recognition of history."

But he said, "No matter how justified, war promises human tragedy."

He also emphasized alternatives to violence, stressing the importance of diplomatic outreach and sanctions with teeth to confront nations such as Iran or North Korea that defy international demands to halt their nuclear programs or those such as Sudan, Congo or Burma that brutalize their citizens.