The War was not pre-emptive. No treaty or Peace Agreement ended the Gulf War of 1991. Only a Ceasefire ended hostilities. Thus under International Law a state of War continued. The Ceasefire Agreement was violated numerous times during the intervening period by the former Regime. In 2002 the Ceasefire was suspended by United States & hostilities resumed. Further discsussion of so-called 'pre-emption' is irrelevent at this point since the former regime is no longer in power.
One must not confuse objectives in war with rationale. The objective was always clearly stated as 'regime change'. To confuse American policy objectives of regime change with rationale for such objectives as WMD, human rights abuses & democratization is putting the cart before the horse.
Wars are not pursued for 'reasons' they are prosecuted to achieve objectives. 'Reasons' for war are for the less initiated who must be convince or cajoled to support the effort. What is important is that the objective be satisfied. Thus removal of Sadam does not in itself achieve regime change. Regime change means supplanting the prior exisitng regime with something in its place, not merely a Transitional or Provisional authority. We would hope a democratic regime would take its place permanently, but history shows democracies are not set up in 6 months or 2 years and then the US can pursue an 'exit strategy'.
France began a policy of regime change toward Germany in 1871, a wish that Germany would become democratic and no threat to its neighbors. The French policy of regime change toward Germany took essentially 74 years and 2 world wars to achieve. France convinced others and built a system of alliances to achieve its purpose. And ultiumately Germany did become democratic. But in 1945 that was hard to see, it still took decades for the world to become convinced Germany was indeed democratic.
The states of the former Soviet Union, the Russian Federation in particular, suppossedly threw off the elements of the old regime more than a decade ago and adopted a democratic form of government. It remains to be seen if the Russian Federation will adopt democracy for its people or if the current period is really more akin to Germany's Weimar Republic.
As for Iraq, our committment is longterm, like it was to Germany, Japan, South Korea & Taiwan. In 50 years Iraq likewise will no longer have to be treated as an adopted child and can rightfully take its place among the community of naitons.