"Accepting Peace Prize, Obama Evokes 'Just War,'" notes the headline in the New York Times, referring to President Obama's speech accepting the Nobel Peace Prize. President Obama did indeed invoke the concept of a "just war." But tellingly, he did not try to argue that the U.S. war in Afghanistan meets the criteria to be judged as a "just war."
A plausible explanation for the President's failure to argue that the war in Afghanistan is a "just war" is that he recognizes that such an argument would not be convincing.
As President Obama noted in his speech, there are criteria involved in the "just war" concept. It isn't just a matter of proclaiming that a war is justified. There are tests.
This matters, because a substantial part of the U.S. and world population subscribes to the theory of "just war." In particular, more than a fifth of the U.S. population are estimated to identify as Catholics. The concept of "just war" - that wars can be considered "just" only if they meet certain criteria - is an official doctrine of the Catholic Church.
Here's part of what the official Catechism of the Catholic Church has to say about this:
2307 The fifth commandment forbids the intentional destruction of human life. Because of the evils and injustices that accompany all war, the Church insistently urges everyone to prayer and to action so that the divine Goodness may free us from the ancient bondage of war.
2308 All citizens and all governments are obliged to work for the avoidance of war.