The Great Depression in Pictures
Hoover Strikes Again: Worldwide Edition
In an ill-conceived attempt to try to aid the bleeding US economy, the William Hawley-Reed Smoot team of senators pushed the Hawley-Smoot Tariff Act of 1930, which were stringent protectionist policies that increased US tariffs, which in turn, decreased exports across the board.
Hoover, with his claim that the worst was behind them, immediately signed it.

Hoover Strikes Again: Worldwide Edition
Besides crushing the agricultural industry, this also caused the Great Depression to spread worldwide.
This would also strongly affect Germany, and many believe helped lead to the rise of Nazism in Germany as well as World War II.