1930 — President Hoover signs the Smoot-Hawley Tariff, raising duties to an all-time high. The United States undergoes a sharp decline in international trade, causing the Depression to deepen.

Elsewhere that year:

• B. J. Palmer establishes Hole in One Theory.
• The National Chiropractic Association is formed through the merger of the ACA and the Universal Chiropractors’ Association.
• Hitler’s Nazi Party emerges as the majority party in the German national elections, winning 107 seats in the Reichstag. German Chancellor, Heinrich Brüning, forms a right-wing coalition government.
• Constantinople is officially renamed Istanbul.
• Sinclair Lewis becomes the first American to win the Nobel Prize in literature.
• Astronomer Clyde W. Tombaugh discovers Pluto.
• Paul Karrer, a Swiss chemist, determines the function and structure of vitamin A.
• The British Parliament debates the Passfield White Paper, which suggests restricting Jewish immigration to Palestine.