The Great Depression started in the United States after a major fall in stock prices that began around September 4, 1929, and became worldwide news with the stock market crash of October 29, 1929 (known as Black Tuesday). Between 1929 and 1932, worldwide gross domestic product (GDP) fell by an estimated 15 %. By comparison, worldwide GDP fell by less than 1 % from 2008 to 2009 during the Great Recession. Some economies started to recover by the mid-1930s. However, in many countries, the negative effects of the Great Depression lasted until the beginning of World War II.

Answer this question based on the passage: when did the great depression begin and why? Let's have some stream of consciousness first.
The relevant information is: The Great Depression started in the United States after a major fall in stock prices that began around September 4, 1929, and became worldwide news with the stock market crash of October 29, 1929 (known as Black Tuesday). So, the answer is a major fall in stock prices that began around September 4 , 1929 , and became worldwide news with the stock market crash of October 29 , 1929.