Which 2020 market crash ended the longest bull market in U.S. history?

The COVID-19 crash ended the longest bull market in U.S. history in 2020.

U.S. stocks entered a bear market in March 2020 as the COVID-19 pandemic spread, governments imposed restrictions, and investors assessed the threat to businesses and global supply chains. The S&P 500 fell about 34% from its February 19 peak to its March 23 low.

The decline was unusually fast. The Dow Jones Industrial Average entered a bear market on March 11, and the S&P 500 followed on March 12. Emergency interest-rate cuts, large fiscal programs, central-bank interventions, and progress toward vaccines helped support a powerful rebound later in the year.

The crash was not caused by one factor alone. Pandemic uncertainty interacted with an oil-price dispute, crowded trading positions, and fears of a deep recession. A bear market means a fall of at least 20% from a recent high; it does not necessarily mean the economy is in a depression.