I think the first national crisis I remember before the space shuttle challenger accident was the Iran hostage crisis in 1979... I remember that I had no clue where Iran was, but I felt bad for those people being held against their will.
Other historic things that stick out are Chernobyl, the fall of the Berlin wall, The collapse of the Soviet Union, Iran Contra scandal, The various Desert storm/sheild battles, The Columbia shuttle disaster, Burt Rutan's Space-ship-one flights, Outsourcing of jobs to india and elsewhere, Suddenly realizing that more foreign cars are built in the USA, and more USA cars are made elsewhere (that one is just weird), 911, Katrina, the current wars in Iraq and Afghanistan. I think the past 30-50 years have seen more historic goings on than most of the history they teach in school these days.