<human>:  Why did the Great Depression start in 1929?
<bot>: The Great Depression started in 1929, because the stock market crashed that year. The crash was caused by a number of factors, including the over-investment in the stock market, the over-expansion of the U.S. economy, and the failure of the Federal Reserve to raise interest rates during the 1920s. The stock market crash caused a major economic downturn, and it took many years for the economy to recover.