As civilians in the Syrian city of Aleppo are battered by airstrikes, ground offensives and shelling, what has happened to the world's responsibility to protect populations under threat?
The Geneva Conventions and the United Nations Security Council were established after World War II to maintain peace and protect people in conflict zones.
But a 21st-century U.N. doctrine called Responsibility to Protect (R2P), set up by the world body's member states to prevent mass killings, has only had limited success.