Lehman Brothers' bankruptcy on September 15, 2008, became a defining trigger of the global financial crisis.
Lehman Brothers filed for Chapter 11 protection after it could not find a buyer or obtain sufficient government support. At the time, it was the largest bankruptcy filing in U.S. history. The firm was heavily exposed to mortgage-related securities and commercial real estate, both of which had suffered as the U.S. housing bubble collapsed.
Lehman's failure shocked financial markets because banks and investors were uncertain about their exposure to one another. Credit markets seized up, stock indexes plunged, and governments around the world introduced emergency lending, guarantees, and bank-rescue programs.
The bankruptcy did not begin the housing crisis; mortgage defaults and financial stress had been building earlier. Bear Stearns had already required a rescue in March 2008. Lehman's collapse nevertheless marked a dramatic escalation and is frequently cited as the moment the crisis became global and systemic.