Going Deep

I am not sure of your opinion toward non-violence and the Christian life, but I have been thinking about this because of some classes and reading. I understand that as Christians we are to be a people who do not respond with violence when we are attacked, basically retaliation. You know the turn the other cheek and the life of Jesus and Paul and how they never hit back. Anyways, I have thinking about the non-violence and pacifism and I have some questions. What are we supposed to do in cases where it is not us being attacked, but someone else? I have heard of getting between the victim and the abusers and I can see the principle there, but what about the cases of mass violence like Rwanda or Dar Fur? If we as Christians are not supposed to support violence then how do we handle these situations? How can we back any troop involvement whether US or UN troops? They are all trained for the same purpose which is to respond with violence. How are we as Christians to respond? I would be interested in your thoughts.