The American middle class...

A fascinating look (in graphs) at the composition of the middle class in the US between 1967 and 2013... Until 2000, the middle class declined because people were moving into the upper class. Since 2000, movement into the lower class drove the shrinkage of the middle class. See:

http://www.nytimes.com/interactive/2015/01/25/upshot/shrinking-middle-class.html?abt=0002&abg=1