It is a commonly held view that the recent war in Iraq was 'illegal'. However, how far is this actually true? Since 1945, so many states have used armed force on so many different occasions (291 wars involving 126 countries), in flagrant violation of the UN Charter, that that authority can only be said to have collapsed.

Massive violation of a particular treaty by numerous states over a prolonged period can be seen as reducing that treaty into a paper rule that is no longer binding. The violations can also be regarded as subsequent custom that creates a new law, supplanting old treaty norms and permitting conduct that was once a violation.

Contrary state practice can also be considered, to have thrown the law into a state of confusion such that legal rules are no longer clear.

If countries had ever truly intended to make the United Nations' use of force binding, they would have made the costs of violation greater than the costs of compliance. But they did not.

Anyone who doubts this observation might consider why North Korea is seeking a non-aggression pact with the US. Such a provision, is supposedly the centrepiece of the UN Charter.

But no one could seriously expect that reassurance to comfort Pyongyang. The Charter has gone the way of the Kellogg-Briand Pact (1928), the treaty by which every major country that would go on to fight in WWII committed itself in not resorting to war as an instrument of national policy.

The truth is that no state has ever accepted a rule, saying that rules can changed only by openly declaring the old rules dead. States do not behave that way. They avoid needless confrontation.

No state has ever declared that the Kellogg-Brian Pact (1928) is no longer a good law, but few would seriously contend that it is. 'Legal' and 'illegal' have ceased to be meaningful terms as applied to the use of force.

There was no UN Security Council authorisation for the use of force by Nato against Yugoslavia in 1998. That action blatantly violated the UN Charter, which does not permit 'humanitarian intervention' any more than it does 'preventive war'.

The US did have all the authority it needed to attack Iraq, not because the UN Security Council authorised it, but because there was no international law forbidding it. It was therefore impossible to act 'unlawfully'.