The onset of the Great Depression is marked by the stock market crash of October 29, 1929, known as Black Tuesday. This event triggered a severe economic downturn that had widespread and devastating effects on the global economy. The crash led to massive financial losses, bank failures, and a significant decline in consumer spending and investment. As businesses failed and unemployment rose, the economic conditions worsened, resulting in prolonged hardship for millions. The Great Depression prompted significant changes in government policy and intervention, influencing economic theories and practices that are still referenced today.