The cause of the Great Depression was due to the crisis that originated in the United States, from the fall of the Wall Street stock market of 1929.
The crack of the 29, was one the biggest crisis ever known that erupted on October 24, 1929. On this date the stock market Wall Street suffered a fall in their prices.
This caused the ruin of many investors, both big businessmen and small shareholders, the closing of companies and banks. This led to unemployment of millions of citizens.
But the problem was not only in New York, this moved to almost every country in the world as a domino effect.