There have been many aspects of my theological beliefs that have led me to pacifism. But the one core belief that has had the greatest impact on these convictions is the straightforward but extremely powerful concept that human life is sacred and must be both protected and respected. This is an idea that should be fairly simple but that unfortunately tends to be forgotten or ignored, either because material interests supersede this respect for life or because that life appears to be a wholly repugnant one (as the recent death of Osama bin Laden has demonstrated).
I think that Catholic social teaching has a great amount to contribute to pacifistic thought principally because it acts as a reminder of the sanctity of life. Removed from a religious context, a person is just another collection of cells. But Catholic social teaching proclaims that humanity means something more. Being human unequivocally means being a brother or sister in a worldwide community. It is our responsibility to uphold and protect members in this community, no matter how physically or morally different they may appear.
This is not to say that pacifism cannot be reached through other routes. Many of the world’s most important pacifists have worked outside of the Catholic tradition. And even in the context of Catholic social teaching there are other forces that can lead one to espouse nonviolence and I am extremely interested in these motivations. But personally, it was the basic belief that human life is sacred and that we are all members of a greater community that led me to pacifism.