What happened?

Sculpture depicting a Great Depression breadline at the Franklin Delano Roosevelt Memorial, Washington, DC

The six months leading up to the stock market crash gave some indication of the financial crisis ahead. The economy had already begun to slump, but no one could forecast the dramatic crash experienced on that October day in 1929. The three years following saw continued decreases in stock prices until, in "late 1932, they had dropped to only about 20 percent of their value in 1929." By 1933, nearly half of America's banks had failed, causing, in large part, a drastic reduction in US manufacturing and unemployment of nearly 30% of the American public.

"About the Great Depression," Modern American Poetry. http://www.english.illinois.edu/maps/depression/about.htm