The repeal in 1999 of the Glass-Steagall act.
"We didn't truly know the dangers of the market, because it was a dark market," says Brooksley Born, the head of an obscure federal regulatory agency -- the Commodity Futures Trading Commission [CFTC] -- who not only warned of the potential for economic meltdown in the late 1990s, but also tried to convince the country's key economic powerbrokers to take actions that could have helped avert the crisis. "They were totally opposed to it," Born says. "That puzzled me. What was it that was in this market that had to be hidden?"
Rules? We don't need no stinking rules!
Yep, that was the removal of the good working regulations.
Without this action the housing price bubble would not have been so big, and banks would not have been tempted to go outside the law.