Resolution 1441.
Nowhere is there anything remotely authorizing the use of force against Iraq.
Not even here:
Decides that false statements or omissions in the declarations submitted by Iraq pursuant to this resolution and failure by Iraq at any time to comply with, and cooperate fully in the implementation of, this resolution shall constitute a further material breach of Iraq’s obligations and will be reported to the Council for assessment in accordance with paragraphs 11 and 12 below;

And besides, there's this!!
Reaffirming the commitment of all Member States to the sovereignty and territorial integrity of Iraq, Kuwait, and the neighbouring States

No wonder Annan said this war was illegal.

The US attacked a sovereign state, unprovoked, under no threat, without waiting for a UN resolution.CQFD.

The fundamental principle of non-interference in the internal matters of a sovereign state is very clear and is the basis behind world peace.
In the Iraq case, there are four parties (or sides or contractants if you wish, I'm not sure of the exact english terminology).
a) Saddam
b) Iraq
c) the US
d) the rest of the world or the UN.

How does a sovereignty principle work?
"b" is left alone, with "a" at its head. Meaning, "a" can do whatever he wants with "b" but in no way can do anything to "c" or "d".
It also means "b" can deal with "a", eliminate him, replace him and neither "c" nor "d" will interfere. There is nothing to do but wait.
Why? Because whoever "a" is, "b" will always want to sell its oil to "c" and "d" who are customers.

But no, "c" thought otherwise and interfered. It's "c" that's losing its soldiers, not "d"; nor is "d" threatened.

Can non-interference be a general rule?
Well, the western christian world has a history of intervening: first to convert the population (with missionaries), then politically and militarily with colonies and now, for humanitarian reasons.
The latter :
It's acceptable IF the country in need asks for the west's help.
It's also acceptable (for humanitarian reasons) IF there is a UN level of acceptance, if countries agree with the principle.
What the US has done in Iraq was to freeze any hope in the near future for humanitarian international contingents.

About the war:

Here, a very good article.

Congress has not declared war on Iraq, no statute authorizes an invasion and Iraq has not attacked the United States, its territories, possessions or armed forces. President Bush’s lawyers have concluded that he needs no new approval from Congress. They cite a 1991 Congressional resolution authorizing the use of force in the Persian Gulf, and the September 14, 2001 Congressional resolution authorizing the use of force against those responsible for the Sept. 11 attacks.

These two resolutions do not provide a basis to circumvent Congressional approval for attacking Iraq. The January 12, 1991 Persian Gulf Resolution authorized the use of force pursuant to U.N. Security Council Resolution 678, which was directed at ensuring the withdrawal of Iraq from Kuwait. That license ended on April 6, 1991, when Iraq formalized a cease-fire and notified the Security Council. The September 14, 2001 resolution authorized the use of armed force “against those responsible for the recent [Sept. 11] attacks against the United States.” There is no evidence that Iraq was responsible for the Sept. 11 attacks.

Raoul