Military action is only legal with UN Security Council approval  Traditionally (by this I mean since 1945!) there are only a couple of ways in which a war is legal. The first is simple; self defence. The UN charter allows “the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations” [1] but this does not fall into that category. Assad is attacking his own people, not another state that is entitled to self defence. No state is able to claim the right to provide self defence for those who Assad is attacking.  A much more viable proposition is to go through the UN Security Council. The charter allows that “The Security Council shall determine the existence of any threat to the peace… Should the Security Council consider that measures provided for in Article 41 [sanctions and other non-forceful methods of applying pressure] would be inadequate or have proved to be inadequate, it may take such action by air, sea, or land forces as may be necessary to maintain or restore international peace and security.” So the UN Security Council certainly could authorise the use of force. Unfortunately a Security Council member, Russia, has already effectively ruled out authorizing military action with its foreign minister urging the US not to repeat “past mistakes” (i.e. Iraq and Libya) and warning “It’s a very dangerous slippery slope that our Western partners have gone on before. I hope common sense prevails.” [2]  [1] United Nations, ‘Chapter VII: Action with respect to threats to the peace, breaches of the peace, and acts of aggression’, Charter of the United Nations, 1945,   [2] Meyer, Henry, ‘Syria Is Headed for Western Strike, Russia Says’, Bloomberg, 26 August 2013,