While I was originally musing over negative events, maybe you could consider Obama's first election as the same sort of major news event (which I suppose could have been negative depending on your perspective)? That would put you right around 12 years old, which is about the time frame I was thinking of.

Then I really have no idea, haha. It's also quite possible that we're so inundated with sensationalized news these days that the idea of one single event sort of stopping people in their tracks just isn't something likely to happen anymore.

The kind of event we're speaking of though is one that strikes at the core of a nation's identity and/or faith in humanity.

I believe these events transcend news. They tend to happen once a decade or two, and as you age the second or third perhaps starts to lose its power.