Intervention would be legitimate  If Syria uses, or looks as if it is about to use, chemical weapons then this would be a clear escalation that would require action. Syria has never signed the Chemical Weapons Convention [1] but it should be considered to be a part of customary international law so binding even on those who have not signed. [2]  The use of chemical weapons would also clearly be an attempt to cause huge numbers of casualties and large scale suffering. In 2005 with the United Nations World Summit the nations of the world signed up to “If a State is manifestly failing to protect its populations, the international community must be prepared to take collective action to protect populations.” [3] So any intervention would be fully justifiable, and indeed should occur as Syria would be demonstrating that it is “failing to protect its populations” by using chemical weapons on them. There is no doubt that the world has a moral responsibility to prevent atrocities in Syria, these atrocities are already happening, but the world cannot stand by while the Syrian government escalates their scale through the use of chemical weapons.  [1] ‘Non-Member States’, Organisation for the Prohibition of Chemical Weapons,   [2] ‘United States of America Practice Relating to Rule 74. Chemical Weapons’, ICRC, 2013,   [3] Office of the Special Adviser on the Prevention of Genocide, ‘The Responsibility to Protect’, United Nations, 2012,