bb asks: "When does a government have the right to interfere in the actions of another government, in order to provide relief for natural ( and other ) disasters, and to preserve human life and liberty?"

The answer is the same as it has been: NEVER. No country has the right to interfere in the internal affairs of another unless invited to do so. That is why the United Nations were formed.

The more relevamnt question is why the UN are so inefficient, and what can be done about that.