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.
Milton Friedman
Friedman rejected the use of fiscal policy as a tool of demand management; and he held that the government's role in the guidance of the economy should be restricted severely. Friedman wrote extensively on the Great Depression, and he termed the 1929–1933 period the Great Contraction. He argued that the Depression had been caused by an ordinary financial shock whose duration and seriousness were greatly increased by the subsequent contraction of the money supply caused by the misguided policies of the directors of the Federal Reserve.