What event is widely regarded as the trigger of the 2008 global stock-market crash?

Lehman Brothers' bankruptcy is widely regarded as the trigger of the 2008 global stock-market crash. The investment bank filed for Chapter 11 protection on September 15, 2008, after failing to find a buyer or secure a government-backed rescue.

Lehman's collapse intensified fears about losses tied to United States mortgages and complex securities. Banks became reluctant to lend to one another, credit markets froze, and equity markets fell sharply around the world. The bankruptcy was the largest in U.S. history at the time.

The crisis had begun before Lehman's failure: Bear Stearns collapsed in March 2008, and housing and credit problems were already spreading. Lehman was therefore a major catalyst rather than the sole cause. The company’s bankruptcy is often confused with the later rescue of insurer AIG, which occurred the following day.