Which global health event was the main catalyst for the stock-market crash of March 2020?

The COVID-19 pandemic was the main catalyst for the stock-market crash of March 2020.

As the coronavirus spread internationally, governments introduced travel restrictions, quarantines, business closures, and other measures that sharply reduced expected economic activity. Investors rapidly repriced companies, commodities, and credit risk, producing an exceptionally fast global sell-off.

The collapse was also intensified by an oil-price dispute between Saudi Arabia and Russia in early March. Major U.S. indexes entered bear-market territory in March, while exchanges repeatedly activated circuit breakers during extreme trading sessions.

Central banks and governments responded with interest-rate cuts, asset-purchase programs, emergency lending, and large fiscal packages. Markets later rebounded, but the pandemic continued to affect employment, supply chains, inflation, and corporate earnings.