REUTERS / Yuya ShinoFinancial markets are rebounding on Monday from the worst selling pressure in months. Friday, the Dow Jones Industrial Average suffered its largest decline since June. Gold fell. Oil fell. Treasury bonds as represented by the iShares 20+ Year Treasury Bond ETF (TLT) returned to levels not seen since June. For investors, it was a very rude awakening from the long, easy, summer doldrums that had kept stocks in the tightest trading range in at least 100 years. Many broadsided by the selloff have two questions: What caused it?