The event in 1929 that marked the beginning of the Great Depression was the stock market crash, specifically on October 29, known as Black Tuesday. This catastrophic event saw billions of dollars in stock value wiped out in a single day, shaking investor confidence and leading to widespread financial panic. The crash triggered a series of bank failures, massive unemployment, and significant declines in consumer spending and industrial production. The Great Depression would last for a decade and have profound and lasting impacts on economies, societies, and governments worldwide.