America wasn't in the war, they started attacking a country that had never attacked them.
That would be like saying it's not a pre-emptive strike if we attacked north korea because they've been at war with south korea for so long.
Yes we do have the benefit of hindsight, and perhaps the western world should of had foresight to see what was happening with germany... they posed an obvious risk and i'm sure if a nation acted in the same way as they did back then they would be attacked, due to this hindsight.
The truth is that while iraq may have been wrong pre-emptive war isn't always wrong, and i'm sure that if another country was threatening peace and stability in the world and not following the rules that govern the international system they would be hit, before an initial attack...