Second, the Fed's easy credit didn't cause the housing bubble because home prices are affected by long-term mortgage rates, not the short-term rates that the Fed influences. From early 2001 to June 2003, the Fed cut the overnight federal funds rate from 6.5 to 1 percent. The idea was to prevent a brutal recession following the "tech bubble" -- a policy Greenspan still supports. The trouble arose when the Fed started raising the federal funds rate in mid-2004 and mortgage rates didn't follow, as they usually did. What unexpectedly kept rates down, Greenspan says, were huge flows of foreign money, generated partially by trade surpluses, into U.S. bonds and mortgages.