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
There is no consensus among economists regarding the motive force for the U.S. economic expansion that continued through most of the Roosevelt years (and the 1937 recession that interrupted it). The common view among most economists is that Roosevelt's New Deal policies either caused or accelerated the recovery, although his policies were never aggressive enough to bring the economy completely out of recession. Some economists have also called attention to the positive effects from expectations of reflation and rising nominal interest rates that Roosevelt's words and actions portended. It was the rollback of those same reflationary policies that led to the interruption of a recession beginning in late 1937. One contributing policy that reversed reflation was the Banking Act of 1935, which effectively raised reserve requirements, causing a monetary contraction that helped to thwart the recovery. GDP returned to its upward trend in 1938.