The Great Depression was an economic depression that affected countries worldwide before the start of World War II. In most countries it started in 1930 and its effects lasted for the next decade up until the middle 1940's for some (after the war). It has been the most widespread, most devastating depression of the 20th century and showed exactly how fragile the economy actually is.
Most historians agree that the Great Depression started with Black Tuesday, with the crash of the stock market in October, 29, 1929. Stock prices have begun to fall in early September already, but the crash of the 29th sent Wall Street in a frenzy and destroyed millions of investors. The devastating effects of this crash caused profits, prices, tax revenue and personal income to drop and international trade decreased with over 50%, which, in turn, affected countries that relied on export. Over 25% of Americans lost their jobs (13 to 15 million people) and in several countries, unemployment skyrocketed to 33% of the population. The economy only started to recover around 1939 and during World War II when the industrial demands of the war boosted American factories.