What is morally right behavior when it comes to self-defense, or the defense of others?

The conundrum comes because of topics currently in world news. Few would argue that defending one's self from an attacker is wrong. Most people believe that if your life or well-being is in danger, you can act to defend yourself, without any qualifications. Most people also believe that if you see someone else being brutally attacked, raped, tortured, or threatened with deadly force, you can come to their aid. In fact, if you turn your back on such a person and do nothing, you are most likely a coward. An individual acting to help others is considered one of the highest forms of altruism. This is how the prototypical hero is born.

So, how does that translate into world affairs? Most people would say that a country has a right to defend itself. That being said, should a country go to the aid of people in another country who are being brutally attacked, raped, tortured, or threatened with deadly force?

If  I saw a woman on the street being brutally beaten and did nothing, I would consider myself guilty of if not the crime itself, of aiding and abetting, and a virtual nodding of consent for the crime to continue. What then of the women in Afghanistan who have acid thrown in their faces for talking to an unmarried man? What of those who are killed in the name of honor for holding hands with a young man whom they have taken a liking to?

If a nation has the power to act and does not, is this not the same thing as if an individual has the power to act and refuses to? For what individual would refuse to come to the aid of someone being attacked if they had the power to do something about it?

I'm not saying there are any right answers here. I've never believed that countries had the same responsibilities as individuals in acting, but as a collective of individuals who would act on an individual basis to stop a brutal attack (and after recent stories in the news about people who have done nothing to stop such attacks, I'm wondering at the veracity of my point), would in not therefore be likely or even expected that the collective would act?