But perhaps the most profound issue surrounding my receipt of this prize is the fact that I am the Commander-in-Chief of the military of a nation in the midst of two wars. One of these wars is winding down. The other is a conflict that America did not seek; one in which we are joined by 42 other countries — including Norway — in an effort to defend ourselves and all nations from further attacks.

Still, we are at war, and I’m responsible for the deployment of thousands of young Americans to battle in a distant land. Some will kill, and some will be killed. And so I come here with an acute sense of the costs of armed conflict — filled with difficult questions about the relationship between war and peace, and our effort to replace one with the other.

Now these questions are not new. War, in one form or another, appeared with the first man. At the dawn of history, its morality was not questioned; it was simply a fact, like drought or disease — the manner in which tribes and then civilizations sought power and settled their differences.

And over time, as codes of law sought to control violence within groups, so did philosophers and clerics and statesmen seek to regulate the destructive power of war. The concept of a “just war” emerged, suggesting that war is justified only when certain conditions were met: if it is waged as a last resort or in self-defense; if the force used is proportional; and if, whenever possible, civilians are spared from violence.

Of course, we know that for most of history, this concept of “just war” was rarely observed. The capacity of human beings to think up new ways to kill one another proved inexhaustible, as did our capacity to exempt from mercy those who look different or pray to a different God. Wars between armies gave way to wars between nations — total wars in which the distinction between combatant and civilian became blurred. In the span of 30 years, such carnage would twice engulf this continent. And while it’s hard to conceive of a cause more just than the defeat of the Third Reich and the Axis powers, World War II was a conflict in which the total number of civilians who died exceeded the number of soldiers who perished.

In the wake of such destruction, and with the advent of the nuclear age, it became clear to victor and vanquished alike that the world needed institutions to prevent another world war. And so, a quarter century after the United States Senate rejected the League of Nations — an idea for which Woodrow Wilson received this prize — America led the world in constructing an architecture to keep the peace: a Marshall Plan and a United Nations, mechanisms to govern the waging of war, treaties to protect human rights, prevent genocide, restrict the most dangerous weapons.

Continued here