Maybe I’m just being present-centric, but I think we don’t remember what happened 100 years ago because there really wasn’t a whole lot going on, at least on the national level. There were all sorts of important trends and movements dealing with industrialization and immigration, but very little in the way of “events” you can really hang your hat on from the end of the Civil War through the 1910’s. Part of it is that national politics had virtually stalled-- both parties’ platforms were virtually identical and it was a whole lot of politics for politics’ sake and bickering over spoils. The period is extremely interesting for economic historians and social historians, but for the typical “great men, great events” that get taught in school, there really wasn’t much going on.
I think that the 1990’s after the fall of the Soviet Union will be viewed as similar, and maybe even up to the present. I don’t think we’re ever going to forget 9/11 per se, but it is my suspicion that as time goes on future generations are not going to regard it as the huge turning point in history that we all assumed it would be. I think on the history textbook level, it got us involved in two relatively minor wars (albeit long and expensive ones) and that’s it-- the “war on terror” didn’t really materialize as the next major phase of history after the Cold War as some people thought it would. As far as I’m concerned, we’re still in the turgid post-Cold War historical dull period. Just like the last third of the 19th century, there’s some incredibly important things going on, but they’re more in the form of long-term trends like globalization than big watershed events.