For the most the United States entered the war with little international support because a clear case as to how the conflict will reduce terror was not made. It was one of the first signs that the war on terror had its limitations. The case against the Taliban in Afghanistan had much more broad international appeal. The Taliban government had violated so many basic rights of the people, harboring and giving shelter to al- Qaeda leaders, as well as publicly commending the attacks of September 11 were all able to give "cover" to members of the international community to participate in the conflict. This was not as present with the war in Iraq. Many feared that reprisal of terrorist attacks in their own countries could be the result of their own participation in the war. At the same time, many felt that the case for war was not being clear and that the United States spirit of willingness and cooperation, more evident in the Afghanistan conflict, struck a more belligerent and defiant tone in this conflict. At the same time, the complex nature of the war, unknown to Americans at the time, was apparent in the statements of some nations, such as the French.
The United States was looking for the approval of the Security Council, a 15 member body within the United Nations, and especially the support of the five permanent members who have veto power.
Russia did not warm to the idea of the war, plus they have often voted against American proposals in the past. The Chinese did not want an unstable Middle East because they depend on the oil reserves there, but were willing to abstain from voting. France felt like the US had not proven its case that there were WMD's present and that Iraq was actually a threat.
Faced with the prospect of losing a UN vote, we withdrew the resolution and acted unilaterally, that is, by ourselves with a few allies we called The Coalition of the Willing.