The Great Depression is the severe, global, long-term economic downturn that began with a stock market crash in October 1929. In the United States, the stock market lost half of its value within a month of the crash’s start and unemployment remained as high as 17% in 1939, 10 years after the crash. The depression followed a decade of spectacular economic growth – the “roaring twenties” – and the U.S. economy didn’t really recover until the build-up to WWII in the 1940s.