Foriegn intervention

Question: When should an international organization like the U.N. or NATO intervene in the domestic  affairs of another country?  I believe the U.S. should support such interventions when there is systematic illegitimate use of power to physically harm a specific class of people that includes harm to women and/or children if and when the legitimate authority of the country in question does not stop the harm.

for example,  an international organization needs to intervene in Syria to stop the systematic slaughter and injury of non-combatants.  The mildest form of intervention should be a total sea, air and land blockade of the country until a non-discriminatory government is in place.  Assad should be held legally liable for crimes against humanity by an international court.

Theoretical example:  President Obama nukes Chicago to conceal past sins, or because he goes insane or for some other irrational reason.  And Congress does not act to impeach.  The rest of the world should care enough to intervene and make sure he is deposed from power. 

I also believe the international community should intervene when one country illegitimately invades another autonomous country in order to seize power. 

If our response to these situations is indifference justified by war weariness or whatever else, we are allowing barbarism to flourish.  Edmund Burke said

“All that is necessary for evil to triumph is for good men to do nothing”.