As Colonel Gaddafi, with his army and air force, his tribal supporters and his propaganda machine, begins to counterattack, only one thing is certain. He is a man utterly without mercy. Will the world stand idly by once he starts to deliver on his threat to "fight to the last man and woman" - and, inferentially, to the last child?
The shadow of Iraq invasion illegality has tainted talk of "liberal interventionism" - unfairly, since Bush was no liberal and Blair has wrongly used it as a retrospective excuse. There was no looming humanitarian crisis in Iraq in March 2003, and the coalition of the over-willing (the US, with Britain, Spain and Australia) explicitly ruled out this justification: they claimed an entitlement to circumvent the Security Council because of a convoluted reading of an earlier resolution and a bizarre "Bush lawyer" claim to the right of self-defence against Saddam's imaginary weapons of mass destruction. The lesson of Iraq, '03, is not that countries such as Britain and Australia should never use force against another, but that never again should they do so in breach of international law.
Which begs the big question, when is there a right - or, more importantly, a duty - to use force to relieve a humanitarian nightmare? The UN charter bans "the use of force against territorial integrity or political independence of any state" other than in individual or collective self-defence, or else with Security Council authorisation after the council has determined under Chapter VII of the charter that a threat or a breach of the peace has occurred.
But the problem is that the "big five" each have a Security Council veto and China and Russia generally oppose intervention other than to liberate invaded states (which was the case with Kuwait when it was invaded by Saddam Hussein).
In my view - contested by some - there is now a narrowly proscribed international law right for states to render assistance to innocent civilians battling for their lives. This right of humanitarian intervention goes back to the "just war" periods in the 16th century: "if tyranny journey becomes so unbearable as to cause the nation to rise, any foreign power is entitled to help an oppressed people that has requested its assistance". Examples of such action are the Tanzanian invasion of Uganda to overthrow Idi Amin; India's incursion to halt genocide and mass rapes in Bangladesh; and the US takeover of Grenada to stop the mayhem after Maurice Bishop's murder.
These actions were, however, justified at the time on very dubious grounds of self-defence and the chief objection to a broadly stated "right of humanitarian intervention" without Security Council approval remains that it is liable to be mistaken for "a right of ideological intervention". Hitler demonstrated its danger of abuse when he invoked it to justify the use of force to protect German minorities from alleged brutality, in Czechoslovakia and then in Poland.
But more recent examples show that a rule of law, built on traditional defences of necessity (excusing unlawful actions taken to prevent serious and imminent peril) and distress (illegality permitted to protect life in an emergency), is developing to allow "coalitions of the willing" to use appropriate force to prevent a humanitarian catastrophe. The two important precedents are the "safe havens" operation by the US, Britain and France, invading Northern Iraq without specific Security Council authority to protect Kurds against violent reprisals threatened by Saddam, and the NATO bombing of Kosovo.
The defects in the Security Council require the acknowledgement of a limited right, without its mandate, for an alliance like NATO to use force to stop the commission of crimes against humanity. That right arises once the council has identified a situation as a threat to world peace (and it has so identified Libya, by referring it unanimously to the ICC prosecutor). To be lawful, the intervention must be at the request of potential victims, for the purpose of stopping crimes against humanity and no mixed or ulterior motive, eg. of obtaining territory or oil. It must be proportionate - no greater force than necessary to achieve a reasonably obtainable objective. Subject to these preconditions, NATO's intervention in a Libyan emergency would be lawful, unless or until it was denounced by majority vote in the Security Council.
A rule of law framed in this way may have to be invoked if Libyans in vast numbers are not to become victims of vengeance from a resurgent Gaddafi. International law is not passed by any parliament: it "emerges" or "crystallises" from state practice, conventions (including human rights conventions), the writings of jurists and the dictates of collective conscience. The duty to stop the mass murder of innocents, as best we can if they request our help, has crystalised sufficiently to make the use of force by NATO not merely legitimate but lawful. It must be a very last resort, after the Security Council fails to act.