What event caused stock markets worldwide to plunge in March 2020 as the COVID-19 pandemic spread?

The event that caused stock markets worldwide to plunge in March 2020 was the COVID-19 pandemic.

As governments introduced travel restrictions, business closures, and stay-at-home measures, investors rapidly revised expectations for economic activity and corporate earnings. The resulting 2020 stock-market crash was intensified by an oil-price dispute between Saudi Arabia and Russia in early March.

Trading was halted by circuit breakers several times in the United States as selling accelerated. On March 16, 2020, the Dow Jones Industrial Average fell 12.9%, one of its worst single-day declines. Central banks and governments then introduced large monetary, fiscal, and emergency-support programs.

The crash is sometimes described as an “overnight” collapse, but global markets fell over several weeks. It also differed from 2008: the initial shock came from a public-health emergency and shutdowns rather than a banking and mortgage-securities crisis.