The following 5-Year Daily ratio charts of the S&P 500 Index compared to Major World Indices shows that the SPX has underperformed all of them since the beginning of this year, and some for the past 1 1/2 to 2 1/2 years.
Price now sits at or near major support levels on all of these ratios. Unless serious buying begins to pour into the SPX, we may see panic selling ensue in U.S. markets. I'd keep a particularly close eye on the German, Japanese and Chinese indices for signs of any potential rotation of money from those markets and into the SPX, since their ratios are at the most extreme levels against the SPX during this 5-year period. Otherwise, the Fed may, very well, consider re-introducing another round of QE to compete with those countries' Central Banks' QE programs.