I don't know about a generally agreed break down, and I'm sure others will add to this, but you could include dynamism, then the explosion of openings information, and the larger explosion of computer databases and analyzers.
Kasparov wrote about a "revolution" in the seventies, although some top players thought that idea was overstated (see his "Kasparov on Modern Chess, Part 1: Revolution in the 70s" which also includes some responses by other top players).
Disclaimer: newbie here
I've read that there was the Classical period of chess that predated the Hypermodern Era (ushered in by the likes of Aron Nimzowitsch and Richard Reti). from here: http://en.wikipedia.org/wiki/Hypermodernism_(chess)
That got me wondering....is there a generally agreed upon historical break down of major chess eras? For example, was there something like a "romantic" era or a "modern" one...or a "renaissance" period, etc.?
TYVM for your knowledge!