The correct answer to this open question is the following.
Some long-term causes of the Great Depression were the overproduction of goods, deep debt due to purchasing on credit, the late intervention of the federal government, and of course, the US stock market crash of October 29, 1929.
In a few words, too much debt incurred by credit buying and the later US stock market crash were major causes of the Great Depression.
To me, the most important cause was the US market crash. This event left millions of Americans without a job and the US started the worst economic period of its existence.
The United States stock market crash of October 1929 started the period called the Great Depression in the United States. After the stock market crash, American citizens lost their jobs, many companies had to close, and banks went into bankruptcy. This period was the worst economic moment for people in the United States. Citizens blamed President Hebert Hoover because he practically did nothing to help them to overcome the difficult situation.