A huge pyramid of debt made possible by deregulation of financial markets, culminating in the 1999 repeal of the Glass-Steagall Act, which had prohibited banks from dealing in high-risk securities. Subprime mortgages were sold to investment companies where they were commingled with prime mortgages to back up new securities that could be touted as both safe and high-yielding. This new debt paper was used by investors as collateral for more loans. When the the subprime homeowners stopped paying, the prices of the mortgage-backed securities fell. Banks demanded that their borrowers pay up or cover their margins. Panicked selling by borrowers further lowered the securities' prices, triggering more margin calls and defaults. The losses piled up at Bear Stearns, Citigroup, Countrywide, Merrill Lynch, Morgan Stanley, and others. The Federal Reserve provided $400 billion in new cash loans to banks and investment firms but Bear Stearns went belly-up anyway, and others came close.