Final answer:
The 1920s ended with the stock market crash in October 1929, marking the onset of the Great Depression, characterized by industry troubles, economic decline, and widespread unemployment.
Step-by-step explanation:
The prosperity of the 1920s ended quite suddenly with the stock market crash on October 24, 1929. This event marked the beginning of the Great Depression, a period of severe economic downturn that would last throughout the 1930s. Industries were already in trouble and agricultural overproduction was rampant prior to the crash. The aftermath saw a contagion effect of panic that further plummeted the economy, with severe impacts such as the Gross National Product declining by over 25%, a $4 billion drop in wages and salaries, and unemployment tripling in just one year. The crash not only signified the market's vulnerability but also the underlying weaknesses within the economy, and the country's inability to manage the sudden economic turmoil without significant government intervention.