woodstock was already teh end of the hippie movement. the vietnam war might have last a few more years, but king and x and jfk had already been killed and woodstock was essentially the mainstream festival to be at, not like the be in's of san francisco.
the 80s? berlin wall came down in 89
As for the noughts, they started off with a bust of 90s first wave interenet technology and w. soon helped roll the ball of shit down the mountain to fuck everythign else up. History could definitely peg this decade as the decline of the american empire. Musically, perhaps the decade of autotune? It is incredible how much pop music uses autotuned vocals these days. Cher was a pioneer, lol.
it would make sense that cultural decades more or less start and end between yeas ending with 0 as people do see the end of a numerical decade as the chance for rebirth.