Which global health event caused the 2020 stock-market crash commonly called the COVID-19 crash?

The COVID-19 pandemic caused the 2020 stock-market crash commonly called the COVID-19 crash.

As the novel coronavirus spread internationally in early 2020, governments introduced travel restrictions, business closures, quarantines, and other measures that sharply reduced economic activity. Investors reassessed corporate earnings, employment, supply chains, energy demand, and the risk of a global recession. The resulting selling pressure produced several historic sessions in February and March.

The S&P 500 entered a bear market on March 12, 2020, and trading was halted several times by automatic circuit breakers. On March 16, the index fell 12%, its worst one-day percentage decline since 1987. Massive fiscal and monetary support, along with improving expectations about vaccines and reopening, helped markets recover rapidly from the March low. The crash was therefore severe but unusually short compared with many earlier market collapses.