Contagious margin calls: How COVID-19 threatened global stock market liquidity

The outbreak of the COVID-19 pandemic caused some of the largest — and fastest — market dislocations in modern history. During the outbreak, liquidity quickly evaporated in a coordinated fashion across global markets. We show that a sudden increase in margin requirements during the pandemic is correlated with the withdrawal of global liquidity providers. These effects are concentrated in securities most exposed to high-frequency market makers, consistent with the binding nature of increased capital constraints.