The Great Depression (1929–1939) was a severe global economic downturn that affected many countries across the world. It became evident after a sharp decline in stock prices in the United States, the largest economy in the world at the time, leading to a period of economic depression. The economic contagion began around September 1929 and led to the Wall Street stock market crash of October (Black Tuesday). This crisis marked the start of a prolonged period of economic hardship characterized by high unemployment rates and widespread business failures.

Between 1929 and 1932, worldwide gross domestic product (GDP) fell by an estimated 15%. By comparison, worldwide GDP fell by less than 1% from 2008 to 2009 during the Great Recession. Some economies started to recover by the mid-1930s. However, in many countries, the negative effects of the Great Depression lasted until the beginning of World War II. Devastating effects were seen in both rich and poor countries with falling personal income, prices, tax revenues, and profits. International trade fell by more than 50%, unemployment in the U.S. rose to 23% and in some countries rose as high as 33%. Cities around the world were hit hard, especially those dependent on heavy industry.