Americas Responsibility Abroad

"250,000 people,100,000 of them children, are under siege in Aleppo, Syria. Bunker buster bombs, cluster munitions, and incendiary weapons are being dropped on them by Russian and Syrian militaries. Does the U.S. have the responsibility to protect civilians and prevent mass casualties on the scale?"
I thought this was the most interesting question from last nights VP debate. Neither candidate gave a satisfactory answer in my opinion. So what does everyone think, does the U.S. have a responsibility to protect people worldwide?