There were many causes of the crisis, with commentators assigning different levels of blame to financial institutions, regulators, credit agencies, government housing policies, and consumers, among others.[1] A proximate cause was the rise in subprime lending. The percentage of lower-quality subprime mortgages originated during a given year rose from the historical 8% or lower range to approximately 20% from 2004 to 2006, with much higher ratios in some parts of the U.S.[2][3] A high percentage of these subprime mortgages, over 90% in 2006 for example, were adjustable-rate mortgages.[4] These two changes were part of a broader trend of lowered lending standards and higher-risk mortgage products.[4][5] Further, U.S. households had become increasingly indebted, with the ratio of debt to disposable personal income rising from 77% in 1990 to 127% at the end of 2007, much of this increase mortgage-related.[6]
When U.S. home prices declined steeply after peaking in mid-2006, borrowers' ability to refinance their loans became more difficult. As adjustable-rate mortgages began to reset at higher interest rates (causing higher monthly payments), mortgage delinquencies soared. Securities backed with mortgages, including subprime mortgages, widely held by financial firms globally, lost most of their value. Global investors also drastically reduced purchases of mortgage-backed debt and other securities as part of a decline in the capacity and willingness of the private financial system to support