Hotel Rwanda

Everyone should see this movie. It raises very interesting ethical/political questions. It’s the story of a man who could not walk away and let people die.
The ethical question is this: If I know someone is being killed and I have the power to stop it, am I ethically obligated to risk my own life to save another?
The political question is this: If such a personal obligation exists, does it extend to nations? Does the United States government, for example, have an ethical obligation to intervene in cases of genocide?