Alex,
I wonder if there is something deeply embedded in the American psyche that causes this absent mindedness? There seems to be some kind of naive optimism and sense of the "promised land" that makes little sense to outsiders looking in.
In fact, the Church of England has just published a report all about how the book of Revelations is being interpreted by Neo-cons and evangelicals as justification for American imperialism and spreading the word of freedom to the darkest recesses of the planet. i.e. american foreign policy and how everyone should embrace an american notion of democracy, like it or not. i.e. the politicians are leveraging misguided beliefs for their own advantage. C of E's interpretation is the opposite - the Book of Revelations was ANTI-imperialist.
The other thing outsiders notice is the hysteria that accompanies disasters in America. Conversely, various american observers were quite amazed at how calm London was in the aftermath of recent terrorist attacks and how quickly it was business as usual. One man who was injured in the blasts was typically stoic and said that he'd be going back to work on the Monday and using the Underground to get there - because he didn't want the rest of his life to be affected by what had happened.
But then maybe it's because our history is littered with war (we must have been at war with the French for the best part of a thousand years, and now we have an ongoing war of words with them - will we ever see eye to eye on anything?

), uprisings, riots and terrorism.
Or maybe it's just as simple as people weren't paying attention in history class!
Jane