The invasion of Iraq by the armed forces of the United States of America and its associates was undertaken under the pretext of "disarming Iraq from Weapons of Mass Destruction (WMD)", but in the course of the invasion the reason for the invasion was changed to "liberation of Iraq from the oppressive government of Saddam Hussain".
As a result of the invasion, the government of Saddam Hussain was removed, and Iraq was left without an effective Iraqi government and under American occupation.
In the interests of the world law and order it is important to establish the legal status of the parties as a result of the above events.
The initial reason for the invasion of "disarming Iraq from the WMD" is not valid, because at present many nation states possess and develop weapons of mass destruction and unless possession and development of WMD is declared a criminal act under International Law, which is applicable to all nation states in equal measure, it is not just to use possession and development of WMD by one nation state as a reason for military action against it, while all other nation states are allowed to possess and develop WMD.
Justification of the American military action on the grounds of self-defence is also invalid, because there is no evidence to indicate that Iraq had attacked or was about to attack the United States of America or any other country.
The justification of "liberating Iraq from the oppressive government of Saddam Hussain" needs, however, a detailed consideration.
It is true that the government of Saddam Hussain was oppressive. It is also true that at present there are no workable legal means of removing oppressive governments. So, given these two facts, is it justifiable for a nation state to remove an oppressive government of another country, and if it is, what is the legal status of the parties in such case?
There are no clearly established principles of International Law for such cases, and to illustrate the principles involved we shall consider an equivalent case involving private individuals, rather than governments.
In a remote part of the world, where there are no police and no courts, "A" is an uncle of two small children, whose parents died, and he took upon himself to look after them. But, while looking after them, he also brutally abuses them.
"A"'s neighbor "B", one day decides to put an end to the abuse of the children by "A". So, he enters "A"'s house and attacks him. "A" resists, and in the course of the struggle "B" kills "A".
Since there is no law in the wilderness where "B" lives, his behaviour is only limited by his own natural sense of right and wrong. So, how should he see himself to be right? He should see himself as a "trustee" acting for the benefit of the children, whom he liberated from abuse, but who now have become dependent on his care for their survival.
So, "B" tidies up the mess caused by the fight, and remains in the house to look after the children, because the children are too small to be left alone without an adult supervision. He also takes reasonable steps to find somebody who would adopt the children, so that he can leave the neighbour's house.
Being in the position of a "trustee", "B" must not use the children's house for his own benefit, but only for the benefit of the children, and the same would apply to any money and food left in the house, it should be used for the benefit of the children.
Now, supposing that we discover evidence that "B" wanted to take possession of "A"'s house for his own benefit in the past - would it change the status of the parties?
It was right for "B" to seek to save the children from brutal oppression by "A", and there being no other legal means available to him, his use of violence is justified. And as long as "B" does not abuse his duties of trustee in any way, his previous intentions are irrelevant, because he has not acted upon them.
Thus, if the Americans have occupied Iraq for the purpose of "liberating the Iraqi people from the oppressive government of Saddam Hussain", as they claim, then their position in Iraq is that of "trustees", acting in the interests of the Iraqi people, until such time that the destruction caused by the military action has been put right and a workable Iraqi government takes over. The Americans have no right to use their presence in Iraq to derive any benefit for themselves, or to seek to install or influence the government of Iraq to their own liking. They should not abuse their status of "trustees".
It is also important to keep account of all the American operations within Iraq, and to publish this account at frequent intervals for public scrutiny. This will help the Americans to demonstrate to the world that they, indeed, are acting as "trustees", rather than as self-seeking predatory invaders using the pretext of "liberation of Iraq" to justify their occupation of the country to advance their own interests.
Whether their invasion of Iraq under the pretext of liberation can be justified depends on whether, there were no other means available to liberate the people of Iraq from oppression.
A mere unintended "good outcome", however, does not justify an unlawful act. And the legality of an act is important and has practical consequences. Failure by the Americans to justify their actions at the start, had given the government of Saddam Hussain a moral and legal right to resist the invasion. It also inspired some Iraqis and foreign sympathizers to fight against the American invasion. This resulted in greater number of casualties and destruction, than it wold have been had the invasion been justified. Anybody, no matter how evil he might be, has right to defend himself against an unjustified attack. But there is no right of self-defence against a lawful authority (e.g. a policeman in the exercise of his duties), nor from a person lawfully using violence to redress an injustice.
This raises the issue of the need for institutions of supra-national law, which would enable people oppressed by their governments to seek redress from such oppression, rather than being left to the mercy of self-appointed vigilantes, who might come to their rescue, if and when it is convenient to them.
Establishment of such institutions would have provided legal means for removal of oppressive governments and made such operations less destructive than wanton sporadic "wars".