Four years after the onset of the financial crisis — in March 2008 Bear Stearns was rescued from failure — we still lack a clear understanding of the underlying causes. Hundreds of studies and books have given us an increasingly detailed picture of what happened without conclusively answering why. Conventional wisdom has advanced competing theories: Wall Street types took too many risks, encouraged by lax government regulation; or, pro-homeownership policies eroded mortgage-lending standards and created the housing bubble.
Actually, both theories are correct — and neither is. It’s true that Wall Street took too many risks while government regulators watched passively; it’s also true that the government’s aggressive promotion of homeownership contributed to real estate speculation. But the fact that these theories are not mutually exclusive suggests that both were consequences of some larger cause. Just so.

Original post: Pinpointing the causes of the U.S. economic crisis