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.
Joseph Stiglitz
Contrary to most economists historians, who argue that tariffs have played only a minor role or not at all in the Great Depression, Stiglitz thinks that the United States should not protect its economy because tariffs contributed to the Great Depression: "Following that, U.S. exports fell by some 50 percent—contributing to our Great Depression".