The significant event that started the Great Depression in 1929 was the stock market crash on October 29, often referred to as Black Tuesday. This catastrophic event followed a period of rampant speculation and inflated stock prices, resulting in a massive sell-off that wiped out billions in wealth. As investors lost confidence, banks failed, businesses closed, and unemployment soared, leading to a severe economic downturn. The Great Depression had far-reaching effects, leading to widespread poverty and changes in government policies, including the New Deal initiatives by President Franklin D. Roosevelt aimed at economic recovery and social reform.