Arthur B. Laffer: Taxes, Depression, and Our Current Troubles - WSJ.com

While Fed policy was undoubtedly important, it was not the primary cause of the Great Depression or the economy's relapse in 1937. The Smoot-Hawley tariff of June 1930 was the catalyst that got the whole process going. It was the largest single increase in taxes on trade during peacetime and precipitated massive retaliation by foreign governments on U.S. products. Huge federal and state tax increases in 1932 followed the initial decline in the economy thus doubling down on the impact of Smoot-Hawley. There were additional large tax increases in 1936 and 1937 that were the proximate cause of the economy's relapse in 1937.