What type of U.S. loans helped trigger the 2008 global financial crisis?

Subprime mortgages helped trigger the 2008 global financial crisis.

These mortgages were made to borrowers considered to have weaker credit profiles or a higher risk of default. During the housing boom, lenders issued large numbers of such loans, including adjustable-rate mortgages whose payments could rise later. When house prices stopped increasing and then fell, many borrowers could no longer refinance or sell at a profit.

Financial institutions had packaged mortgages into securities and distributed the risks through the global financial system. As defaults increased, the value of many mortgage-related assets became uncertain. Banks reduced lending to one another, credit tightened, and losses spread beyond the housing market.

Subprime mortgages were an important cause, but not the only one. Excessive borrowing, weak underwriting, complex securities, credit-rating failures, and inadequate risk management also contributed to the crisis.