I have come to the arbitrary conclusion that while December 31, 1999 marked the official end of the 20th century, September 11, 2001 marked the actual end of the 20th century, or at least serves as a pivot between the world as we knew it (or the world we thought we knew), and this new and frightening epoch that is still unfolding and making itself known to us.

For what it's worth, here's my two cents on 9/11, from a 2015 blog post:

http://jamesdeagle.blogspot.com/2015/09/911.html