I thought that President Obama did a good job in his acceptance speech for the Nobel Prize. He basically gave a very Catholic speech. It was an articulate, realistic view of the world and he framed it in Catholic Social Teaching’s concept of the “Just War Doctrine.”
There are basically two ways that Catholic thought looks at war and any other kind of violence. Both are based on the Judeo-Christian mandate“You shall not kill.” The first is pacifism. This was practiced by the early Christians who felt that any violence, even in self defense, was against the law of Christ to “love one another.” A small minority of Christians still espouse this teaching today. Dorothy Day and the Catholic Worker Movement is an example of this: www.catholicworker.org Another group that believes in pacifism is Pax Christi. You can see more about them here: www.paxchristiusa.org. A recent column by John Dear, SJ demonstrates how this pacifistic view plays out in the present political context: http://ncronline.org/blogs/road-peace/our-new-war-president.
The second Catholic perspective on war and violence is based on the concept of self-defense. Violence is permissible, even obligatory, if one is defending oneself or another from an aggressor. The intention here is not to kill the aggressor but in the process of defending oneself, harm or death may occur. This principle applies to war, the death penalty and any kind of repulsion of attacks. There are conditions that must be followed. See them in detail here: http://www.ewtn.com/expert/answers/just_war.htm.
Applying the principles of just war theory to an actual conflict is very difficult and even contentious. The Vatican, for example, held that both the first Iraq War and the second did not meet the criteria for a just war. Most theologians are in agreement that WWII did meet the criteria. Wars have changed over the centuries. The advent of nuclear bombs, where mostly innocents would be killed, has changed the lay of the land (One of the criterion for going to war is that few if any civilians would be swept up in the killing.) Another factor making it difficult to apply the criteria is the prevalence of terrorism where there is often no identifiable enemy in a particular nation. Is it possible to do violence to people who haven’t yet actually threatened us with an act of aggression, but we know that they will in the future? These are difficult questions.