Faced with having to put more capital against lower rated securities, investors such as banks, pension funds and insurance companies sought to sell their residential mortgage-backed securities (RMBS) and collateralized debt obligation (CDO) holdings. The value of these securities held by financial firms declined, and the market for new subprime securitizations dried up. Some academics and industry observers have argued that the rating agencies' mass downgrades were part of the "perfect storm" of events leading up to the financial crisis in 2008.