I tend to think of the "modern world" as starting with the fall of the Berlin Wall in 1989, but now that I am beginning to work with adults with graduate degrees that weren't even born then, it's beginning to be a bit absurd.
Berlin wall? Imagine my distress at having tuned in to the modern world during the Watergate fiasco. My father had to explain to me that it was the name of a hotel and not some sort of earthworks.