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.
Economic history of the United States
Following the stock market crash, the worldwide economy plunged into the Great Depression. The U.S. money supply began to contract by one-third. The protectionist Smoot–Hawley Tariff Act incited retaliation by Canada, Britain, Germany and other trading partners. Congress, in 1932, worried about the rapidly growing deficit and national debt, and raised income tax rates. Economists generally agree that these measures deepened an already serious crisis. By 1932, the unemployment rate was 25%. Conditions were worse in heavy industry, lumbering, export agriculture (cotton, wheat, tobacco), and mining. Conditions were not quite as bad in white collar sectors and in light manufacturing.