This is my deep (or twisted, depending on your point of view) philosophy...America has a) always been afraid of a "sneak attack" b) always has to have a "boogie man" and c) loves a good conspiracy (good being a subjective term)
A. Going back to the Spanish American war, there was the Maine bombed in Cuba, the Lusitania, Pearl Harbor, the Gulf of Tonkin, and 9/11. All sneak attacks that got us into wars. Could be other examples, feel free to help me out. The real irony is, as you said, that Bush invaded Iraq to PREVENT another sneak attack. All intel, not only from the U.S. administration, but from foreign governments and with the backing of such Congressional leaders as Hillary Clinton indicated that it was time to call Saddam's bluff and remove the threat.
B. You've got to have a boogie man that you're either in a cold or hot war with. Too many examples here, fairly self explanatory. Feel free to add to the list, though.
C. All of the "sneak attacks" that I cited in paragraph A had associated conspiracy theories, along with such other things as JFK's assassination and the moon landing. Again, feel free to cite others.