Who/What Caused the Great Depression?

Milton Friedman weighs in on the question.

From 1929-1933 the total quantity of currency (M2) in the US declined by 1/3. The total number of banks fell by 1/3. There never was a moment when the Federal Reserve couldn't have controlled the quantity of currency in circulation in the nation. -Friedman

The Great Depression wasn't caused by private business. It was caused by a failure in government.