What caused the 20072008 decline in housing prices?

What caused the 20072008 decline in housing prices?
too much supply (overbuilt) for too little demand coupled with a credit crunch which led to higher interest rates on mortgages (especially hurting ARM holders whose variable reset was much higher than what they were used to paying). It also made it more difficult for people with less-than-perfect credit obtain a mortgage at a reasonable rate. Therefore as people wanted to sell their homes, buyers were unable to obtain loans to purchase. This forced sellers to lower their home prices in a vicious circle that ultimately led to the actual market value of many peoples' homes to drop below the amount of their mortgage menaing there was negative equity in the home. At the same time the stock market dropped significantly and unemployment rose to a current 6.1%.. with more people unemployed, more people were missing their mortgage payments, especially those with lower credit ratings (i.e. sub-prime). Mortgage lenders were selling their loans to banks who packaged them up with other mortgages.. prime and sub-prime, and loans to create Mortgage-Backed Securities which were in turn sold to other banks, investors, and governments around the world. These securities, including CDOs and CLOs were rated AAA (the highest quality, lowest risk) by various credit rating agencies. Once people starting defaulting on the sub-prime loans the faith in these mortgage backed securities weakened and became riskier and were no longer AAA rated. This caused a huge downward spiral in their price as no bank wanted to trade these anymore and could not liquidate positions.