On Black Monday, October 28, 1929, the Dow declined nearly 13 percent. On the following day, Black Tuesday, the market dropped nearly 12 percent. By mid-November, the Dow had lost almost half of its value. The slide continued through the summer of 1932, when the Dow closed at 41.22, its lowest value of the twentieth century, 89 percent below its peak. The Dow did not return to its pre-crash heights until November 1954.

The Tariff Act of 1930, also known as the Smoot–Hawley Tariff Act, was a protectionist trade measure signed into law in the United States by President Herbert Hoover on June 17, 1930. Named after its chief congressional sponsors, Senator Reed Smoot and Representative Willis C. Hawley, the act raised tariffs on over 20,000 imported goods in an effort to shield American industries from foreign competition during the onset of the Great Depression, which had started in October 1929.

Hoover signed the bill against the advice of many senior economists, yielding to pressure from his party and business leaders. Intended to bolster domestic employment and manufacturing, the tariffs instead deepened the Depression because the U.S.'s trading partners retaliated with tariffs of their own, leading to U.S. exports and global trade plummeting. Economists and historians widely regard the act as a policy misstep, and it remains a cautionary example of protectionist policy in modern economic debates. It was followed by more liberal trade agreements, such as the Reciprocal Trade Agreements Act of 1934.