Well.. one source says:
Sometime after the panic of 1929 a reporter asked JP Morgan what caused all this to happen. He said " someone asked for a dollar".
(His point being that the banks were so leveraged that one too many people withdrew one too many dollars. Then that first domino fell. And the rest is history.)
Maybe years from now it will be said that the domino that caused the crash of 2008 was some idiot Senator from New York and his devious scheme to crash a large bank before the elections?
Can a knowledgeable person recommend a good book that explains what happened to cause the great depression?