Short answers, pulled from the story.
The Great Depression began on the 24th of October 1929 when the American stock market crashed 11% at the opening bell, an event known as Black Thursday. This financial crash triggered a global economic downturn that lasted from 1929 to 1939.
The gold standard acted as a primary transmission mechanism that spread the downturn worldwide and forced countries to reduce their money supply and domestic price levels. Countries that abandoned the gold standard early, such as the United Kingdom in September 1931, experienced relatively mild recessions and early recoveries compared to those that remained on it.
The crisis caused unemployment in Germany to rise to nearly 30% and fueled political extremism that paved the way for Adolf Hitler's Nazi Party to rise to power in 1933. The financial crisis escalated out of control in mid-1931, starting with the collapse of the Credit Anstalt in Vienna in May.
By 1933, the U.S. unemployment rate had risen to 25% and 9,000 of its 25,000 banks had gone out of business. About one-third of farmers had lost their land, leaving the nation in ruins.
The outbreak of World War II in 1939 ended the Depression by stimulating factory production and absorbing large numbers of unemployed men into the military. The American mobilization for World War II at the end of 1941 moved approximately 10 million people out of the civilian labor force and into the war.