The Roman Empire did not actually fall. It was taken over by a church.
I suppose, at a stretch, it could happen to the U.S. too.

The plethora of helmet-saved-my-life anecdotes begins to not ring true eventually. Not only because they did not exist before bicycle helmets in any degree. In my estimation they are like the observations of someone who wears hearing protectors or an industrial helmet and begins to notice how often he bumps them on things, but then concludes those objects would have hit his ears or head. The sound is amplified and the space your head has to negotiate is greater, hence the distorted perception of having been saved from injury.