Which 2008 US housing-market problem was the central trigger of the global stock-market crash?

The subprime mortgage crisis was the central trigger of the 2008 global stock-market crash. It began with defaults and falling values in US home loans made to borrowers with weaker credit profiles.

During the housing boom, lenders originated large volumes of subprime mortgages, many with adjustable rates or limited documentation. These loans were bundled into mortgage-backed securities and related products distributed through the financial system. When house prices fell and refinancing became difficult, delinquencies rose and the value of those securities plunged.

Banks and investors then faced losses, uncertainty, and a shortage of short-term funding. The crisis contributed to the failures or rescues of major institutions, including Lehman Brothers, AIG, and Washington Mutual. The phrase does not mean every mortgage was subprime; it identifies a specific high-risk segment whose losses were magnified by securitization and leverage.