US President Barack Obama accepted the Nobel Peace Prize presented to him at a formal ceremony in Oslo on Thursday afternoon.
"The instruments of war have a role to play in preserving the peace," said Obama in his acceptance speech, stating that war and peace have been interwoven since that dawn of man.
"War in one form or another appeared with the first man â€¦ [it then became] the manner in which tribes and then civilizations sought power and settled their differences."
The US president also referred in his speech to the wars in Iraq and Afghanistan. "The world rallied around America after 9/11," he said.
Obama suggested that the wars of history, in which "the concept of just war was rarely observed," were giving way to wars in which "the purpose of military action exceeds self-defense."