" 

 There has been a debate in Britain over the last month if HMG had clear legal advice over the British involvement in the Iraq invasion. But no one in Britain says that because the British invasion of Iraq may have needed another UN resolution to be legal, that it follows that Britian's participation in the Falklands War was also illegal, because it was conducted under Article 51 of the UN Charter and did not need a UN resolution to be legal. Neither is anyone is saying that because the liberation of Q8 could be justified under Article 51, that the invasion of Iraq 10 years later is justified. The invasion of Iraq can not be expanded into a general rule ""that a belligerent has to have a UN resolution to legalise a belligerent's participation in a war"". It depends on the circumstances of the war as to what makes a belligerent's participation legal under its international treaty obligations.  "