The economic slowdown in the 1920's actually started in 1927 for most Americans, and unemployment started rising, just a few years after the 1919-1921 recession after WW I. The stock market promised higher returns than investing in real businesses and sucked up money like a sponge, just like all the other 'booms' have, before and after the 1920's, including the current one. The economy began turning around within months of FDR's election, and by 1937 was almost back to pre-Depression levels of output.
As always, large increases in productivity rates caused employment to lag way behind, a recurrent problem throughout the 19th and 20th century, right up to today. Pile 'outsourcing' to 'business friendly' slave labor and sweatshop countries, like Red China and Viet Nam, Mexico, etc. through various scams like NAFTA, CAFTA, et al, and the domestic economy ends up with almost no connection to the Wall Street and Greenwich, Conn. economy people like Mitt Romney and Warren Buffet live in.
I see Frank weighed in to provide a fine example of the clueless cognitive dissonance I was talking about.
Thanks, Frank!