Causes of the Great Depression
Second, there are the monetarists, who believe that the Great Depression started as an ordinary recession, but that significant policy mistakes by monetary authorities (especially the Federal Reserve) caused a shrinking of the money supply which greatly exacerbated the economic situation, causing a recession to descend into the Great Depression. Related to this explanation are those who point to debt deflation causing those who borrow to owe ever more in real terms.
Great Depression
Two economists of the 1920s, Waddill Catchings and William Trufant Foster, popularized a theory that influenced many policy makers, including Herbert Hoover, Henry A. Wallace, Paul Douglas, and Marriner Eccles. It held the economy produced more than it consumed, because the consumers did not have enough income. Thus the unequal distribution of wealth throughout the 1920s caused the Great Depression.