The US housing bubble was actually caused by regional government restriction of land supply coupled with federal laws that increased the demand for homes.
The regions affected were properties in the metropolitan areas of the east and west coast.  The local areas restricted building under the guise of “smart growth” or through restrictive zoning laws and planning commissions, whatever the name, the net effect was to restrict land supply and thus drive up the cost of land in these areas.
Starting with the Community Reinvestment Act (CRA) of 1977 Congress forced banks to give loans they would not otherwise give. This raised demand and gathered momentum after Reagan left office when the White House pressured HUD, the Attorney General, The Federal Reserve and all institutions with regulatory authority over banks to pressure them to make loans to low income Afro-Americans using racial statistics to determine whether the banks were compliant. Jonathan R. Macey, a professor at Cornell University Law School, stated "No bank, no matter what it does, is safe from charges of discrimination. And this is true despite the fact that the industry spends over half of its profits to comply with regulations."
In 1995 these regulating agencies required the use of “innovative or flexible” lending practices. Fannie Mae and Freddie Mac were pressured to lower their down payment requirement as well. In 2002 Congress passed the American Dream Down Payment Act which subsidized the down payments of low income home buyers. These loans were encouraged by the Federal Reserve which had lowered the interest it charges to 1%.
The Federal Reserve began raising the rates in 2004. By 2006 the rates were 5.25% which lowered the demand and for those on adjustable rate mortgages increased their payments until they couldn’t pay anymore. The foreclosures followed increasing supply dropping housing prices further.
The mortgages had been bundled together and sold on Wall Street to investors and other countries who were looking for a higher return than the 1% offered by Federal Reserve. Instead of the limited regions suffering the housing drop it was felt around the world. The same Federal Reserve that had enforced sanctions on those banks who didn’t give these loans now suggested bank take overs and more regulations. The Congressmen who had pushed the hardest to create these “subprime loans” now blamed Wall Street for selling them. (So far none of these laws have been repealed. They are simply not being enforced.)
In 1995, Fannie Mae and Freddie Mac began receiving affordable housing credit for buying subprime securities 
Some borrowers got around downpayment requirements by using seller-funded downpayment assistance programs (DPA), in which a seller gives money to a charitable organizations that then give the money to them. From 2000 through 2006, more than 650,000 buyers got their down payments through nonprofits. According to a Government Accountability Office study, there are higher default and foreclosure rates for these mortgages. The study also showed that sellers inflated home prices to recoup their contributions to the nonprofits. On May 4, 2006 the IRS ruled that such plans are no longer eligible for non-profit status due to the circular nature of the cash flow, in which the seller pays the charity a "fee" after closing. On October 31, 2007 the Department of Housing and Urban Development adopted new regulations banning so-called "seller-funded" downpayment programs. Most must cease providing grants on FHA loans immediately; one can operate until March 31, 2008.