It didn't happen, at least not like it's been reported; I refer you to @oldoneeye's response. Also, the stated spark wasn't that, it was the supposed immediate threat of further terrorist actions against Americans that had to be stopped. When asked for proof of this, we get silence; there is no proof, just like there was no proof for Saddam's weapons of mass destruction. Lastly, and most importantly in my opinion, any military or other violent action against America should be seen as purely defensive action; they didn't invade America.